There are probably far more rumors and bits of speculation to analyze regarding the Freeza arc, but doing so somewhat falls into that same trap of giving it undue importance. That being said, onward into the Cell arc!
Toriyama didn’t originally plan on No. 17, No. 18, or Cell appearing
After all the unfounded rumors about the Freeza arc, it may shock you to learn that this rumor is in fact 100% true! As he says in Shenlong Times #2, Toriyama was originally going to have 19 and 20 be the villains of the arc, but when that did not go over too well he brought out 17 and 18, then finally Cell.
Before delving deeper into that though, it is probably best to explain Akira Toriyama’s editors. Toriyama had three editors over the course of Dragon Ball, but he only had one editor at any given time. His first editor was Kazuhiko Torishima, who was also the man at Jump who first discovered Toriyama, and who served as his editor for all of Dr. Slump. Torishima was editor from the beginning of Dragon Ball up until the end of the 23rd Tenka’ichi Budōkai. Toriyama’s second editor was Yū Kondō, who took over during the Saiyan arc and lasted up until when Cell reached his perfect form. The third editor was Fuyuto Takeda, who took over when perfect Cell appeared and lasted until Dragon Ball‘s end (he has also served as editor for Toriyama’s post-Dragon Ball work). It was commonly rumored at Jump that Toriyama incorporated his editors into Dragon Ball as villains. Torishima was rumored to be the basis for Piccolo Daimaō , while Kondō was rumored to be the basis for Freeza, and Takeda the basis for Majin Boo. These rumors were prevalent enough to even be mentioned in Shenlong Times #2, where the editors discussed them briefly (Kondō, for his part, had always imagined himself as the basis for Trunks). However, when asked about this in Dragon Ball Forever, Toriyama denied consciously basing these characters on his editors, but admitted that he might have done so subconsciously. At any rate, Torishima is undoubtedly the basis for the villainous Doctor Mashirito in Dr. Slump (To-ri-shi-ma ›› Ma-shi-ri-to).
Torishima himself is an interesting character. After he left as Toriyama’s editor, he went on to become head editor of V-Jump in 1993. In 1996, shortly after Dragon Ball ended, he became editor-in-chief of Weekly Shōnen Jump, and under his leadership Jump began coming out with new hits like Yu-Gi-Oh!, One Piece, and Naruto. In 2001 he became the head editor of Weekly Shōnen Jump, Monthly Jump, and V-Jump, and in 2004 he joined Shueisha’s board of directors.
Dragon Ball fans tend to treat Toriyama’s three editors as simply a group, as if they had each simultaneously served as his editor during Dragon Ball‘s entire run. There are a couple of reasons for this. First is simply confusion due to there not being all that much information on them out there. Another reason is that Viz’s translations sometimes have Toriyama refer to his “editors” in plural, as if he had more than one at once. Part of the problem is how Japanese lacks a real plural, making it sometimes ambiguous how many people are intended, but other times it is Viz being a little strange. For instance, in their translation of Toriyama’s closing remarks from Dragon Ball‘s final chapter, they have Toriyama say that “My editors have agreed to let me end this manga”, whereas in the original Toriyama talks about getting kankeisha — “those involved” — to let him end the series. Toriyama’s editor would be one of those involved of course, but there would probably be others, and at the time Toriyama would only have had a single editor, Fuyuto Takeda, not multiple ones. Another reason fans may tend to think Toriyama had all three editors at once is because Greg Werner’s translation of Toriyama’s roundtable talk with his editors in Shenlong Times #2 which Werner featured on his “Ultimate DBZ Info Site” was mistranslated so that the editors talked as if this had been the case.
At this point, you probably now have the context to appreciate this Shenlong Times #2 excerpt properly:
Akira Toriyama: At that time it began to be more fun to think up the story than to draw the pictures. But with the story, I basically only thought of each chapter. That’s why I end up getting caught in these quagmires. (laughs) Around the time of Trunks’ time travel, it was dreadful. I kept drawing, and it just got more and more incoherent.
Kazuhiko Torishima: You only got away with that because Kondō was your editor. I can’t stand that kind of troublesome stuff. (laughs)
Akira Toriyama: You’re terrible to say that, Torishima-san. Right around then was when the Androids No. 19 and No. 20 appeared. You weren’t my editor or anything anymore, but you specifically called me to say “I thought that the enemies had finally come, but aren’t these just a geezer and a fatso?” (laughs) In truth, I hadn’t had plans for anyone but No. 19 and No. 20 to appear. But there was no helping it, so I brought out No. 17 and No. 18. Then you called me up and said “What, this time it’s just some brats?” So I brought out Cell. (laughs)
Fuyuto Takeda: So you hadn’t planned on Cell appearing at all?
Akira Toriyama: That’s right. I liked No. 19 and No. 20 just fine. And I liked the initial Cell fine as well.
Fuyuto Takeda: The bug-like one?
Akira Toriyama: But Kondō-san said “He looks ugly. Of course, he can transform.”, so I had no choice but to transform him into his second-form.
Yū Kondō: Was that how it was?
Akira Toriyama: And then you were really awful, Kondō-san. “This time he looks like a moron, doesn’t he? Hurry up and make him into his perfect-form.” you said.
Yū Kondō: But he really did look like a moron. (laughs)
Akira Toriyama: With second-form Cell as well, I liked him well enough. Actually, I had wanted him to play a more active role. But since I was told he looked stupid, I had no choice but to change him. (laughs) So I made him into his cool-looking perfect form, which was to Kondō-san‘s liking.
When fans tell this story, they often say that “Toriyama’s editor(s)” made him introduce No. 17, No. 18, and Cell, but as you can see this is only half true. Rather, it was Torishima, who at this point was editor of V-Jump and not Toriyama’s editor anymore, who called Toriyama up to complain about No. 19 and No. 20, and then later No. 17 and No. 18. Nothing is said about Toriyama’s actual editor at the time, Kondō, having any objections to No. 19 and No. 20 being the main villains. Rather, what Kondō objected to was Cell’s initial design, and then his second form’s design. The editors seem to take undue criticism from fans for being meddling fools who do nothing but mess up Toriyama’s perfect vision, when in reality one of the only confirmed instances of their interference was in preventing the Cell arc from climaxing in a confrontation between the Z-Warriors and some “geezer”.
It is rather interesting that Toriyama would feel that “there was no helping it” and he had to bring in new villains simply because someone who was no longer his editor voiced his disapproval of the current bad guys. As mentioned, Torishima went on to become a significant figure at Jump and Shueisha, but at the time he was editor of V-Jump — it is unclear how that would affect his relationship to/with Toriyama. Perhaps his position as head of one of Shueisha’s major magazines simply gave him the right to monkey with Toriyama, even if he was not actually head of the magazine which Dragon Ball happened to be running in. Maybe Toriyama was simply conditioned by this point to listen to whatever Torishima said, even if he did not technically have the authority to boss him around any more. Maybe he just knew in his heart of hearts that Torishima was right and that 19 and 20 kinda sucked. Maybe it is a Japanese thing. Maybe it is a Toriyama thing. Who knows?
Toriyama planned on ending the series at the Cell arc
Part of the whole package of rumors about Toriyama’s thwarted plans of ending the series with the Freeza arc is that, once that plan fell through, he then tried to end it after the Cell Games only to fail once more. All the same things that can be said about the supposed Freeza ending can be said here too: Toriyama has never said such a thing in interviews. He would not have been simply told at the last minute that he would not be allowed to end the series there, so pointing out how climatic the end of the Cell arc feels is irrelevant. If Toriyama had been given the option to end it there, he probably would have. It is unlikely that he would have said “No, I must continue! For I have an artistic vision burning inside me, that I must let out! A vision of a bubblegum monster beating up on a little kid with really long hair and no eyebrows!”… but there is simply no evidence that he actually thought he was going to be given that option while writing that storyline.
Dragon Ball Kai concluding with Cell proves that this was the original vision for an ending
Unfortunately, now that Dragon Ball Kai originally “ended” with the Cell arc before being revived in 2014 for the Majin Boo arc, it is probable that some people might and will take this as a sign that Toriyama really had planned to end the manga with Cell. However, while it is true that early on Kai was promoted as a “Toriyama original cut” of the anime, there is nothing to suggest that he has had any actual hands-on involvement with the series, other than maybe coming up with the name “Kai”. When Toei Animation says “Toriyama original cut”, they seem to just mean that the series more closely follows the original manga than Dragon Ball Z had, by cutting out much of Z‘s anime-only filler. There is no reason or evidence to think that Kai first ending at the Cell arc has anything to do with Toriyama’s input or original vision for the story. Rather, Kai‘s abrupt end can far more convincingly be explained by the continuing decrease in sales for everything Dragon Ball-related — despite Kai having fairly good ratings during its run, its home releases and tie-in games had sold poorly, with sales figures only leveling off once the series was no longer on television.
Despite being billed as closer to the manga, Dragon Ball Kai (which does not have the “Z” in its title in Japan) starts at the Saiyan story arc rather than with Goku meeting Bulma; the first 194 chapters of the manga are represented only by a brief montage in the first episode. Does this mean that Toriyama originally intended to start the manga with Raditz reaching Earth? Obviously that is absurd. We know that Toriyama originally never intended to go beyond that first search for the Dragon Balls, and had no idea at the beginning that Goku was a Saiyan. Most likely, the reason Kai starts with the “Z” portion of the story is simply because that is the most popular portion of the series, and beyond that, happened to tie in with the 20th anniversary of the “Z” portion of the TV series specifically. By extension, besides poor sales, the reason Kai will not be covering the Boo arc could be because that portion of the series has never been as popular as the Saiyan, Freeza, or Cell story arcs. It may even be possible that from the start Toei Animation only planned on Kai covering the Saiyan through Cell portion of the series due to its popularity.
Kai aside, there is probably more to analyze here, but it would follow the exact same formula as the Freeza arc — most of what was stated there applies here as well (outside of talking about very specific rumors like Goku dying and whatnot).
It may be worth noting as one final point for the Cell arc that there was a two-week gap between the end of the arc and the start of the Majin Boo arc, but that is only because Weekly Shōnen Jump itself took a break for one week (May 16th-22nd, 1993).