Too bad potential varies with time. Piccolo's potential in buu arc is not the same as his potential in RoF arc. See how piccolo surpassed raditz in 6 months while he couldn't get to a level even close to him in 5 years of training, when he wanted to kill goku.
Also, I'm not even putting piccolo above SS3 goku (buu arc) who is the weakest SS3 in series (canon & non-canon material considered).
Well... Potential, for starters, generally decreases for humans in the real world (the older you get, I suppose you get the general idea). Nevertheless, strictly speaking we'd be talking about a Namekian, so who knows.
In any way, you could still argue that every time Piccolo had some jump he always had some sort of new catalyst: he changed and upgraded training regime/ added in every saga, while from Buu Saga to today he simply trained like he always had. And it's not like I'm
entirely against the idea that you may have "bigger potential", or rather, that you could gain more from one kind of training than another.
However, you're basically suggesting that Piccolo's potential could rise from one day to another without any proper explanation by doing the same things he always did. In short, you're just saying that "it happened" without adding anything else.
Piccolo from DB to Saiyan saga = trains with Kaio, Namek = he gets Nail, Androids = he trains with his new body, Cell = he gets Kami, Cell Games = he trains with his new body and he's weaker than Cell. From Cell Games to Buu Saga = keeps doing the same training like with the same old body and he is still weaker than Cell. So, most likely, the story tentatively implied that Piccolo could get only marginally stronger by training or that in his current state he hit his plateau either in the ROSAT or some time later, still being weaker than Buu Arc Gohan/ Cell.
So,
if as far as we know Piccolo trained as it always did, you either have to argue that some special training/ plot device
x we had no chance to see happened on screen (which is a Devil's Proof, basically) or argue that Piccolo's "potential", as you intend it, could rise or lower from one day to another without a plot device, which sounds again like a non-explanation. It'd be different if we had been told that... I dunno, the older a Namekian gets the better they get.
For those of you who actually subscribe to the theory of Goku having two bases, aren't you ranting about Piccolo's insane power boost because said milestone lacks explanation and/or proof?
Well, while I'm more in line with the Goku is serious or not serious (at least to me, though, the "two bases idea" is simply Goku using as much ki as he wants to do this or that), there is one crucial difference: the Piccolo is uber strong theory creates either plotholes or bad writing that can go from "really bad" to "somewhat bad".
The other one is contrived and counter-intuitive, but it helps evidently to put some minds with Super's writing. It would be still bad writing to quite some people, most likely ("huge lack of exposition", namely). However, and that's the thing to stress, it
wouldn't be a plothole in the sense that it would not create contradictions.
As far as we know because Piccolo couldn't have killed Kid Buu in the anime by training in the ROSAT either by himself or with Gotenks because he didn't do it, and it's hard to think that things have changed with the current outline of the plot (and without out-of-universe explanations). So if Piccolo suddenly became stronger than Kid Buu, it would arguably be a contradiction with the material the story presented long time readers/viewers of DB.
That is not counting two things:
A. The way Toriyama presented the characters (the "always a third weel" Piccolo" and the "crazy strong" Buu).
B. The possibility of SS Gohan being ROF is stronger than SS3 Goku, of course, and that, by training with Gohan, Piccolo could have become vastly stronger himself.
I do think that too sounds pretty hard to believe, gut feelings aside; Gohan expressly says that he is still le-learning the basics right before the tourney takes place. Plus, in the anime, Goku is supposed to be the strongest in the beginning of Super. So Gohan would have had to surpass Goku in-between episode 2 and 30-something and then get weaker (by training? Not training? It looks like he never trains), and
yet strong enough for Piccolo to surpass/rise to SS3 Goku's power too.
Sure enough, Piccolo
could be stronger than anyone in the Buu Saga in Toriyama's mind. It wouldn't change that it would be
objectively inconsistent with what the story showed us so far, or bad writing in the sense that it lacks a proper explanation that justifies the scenario we have been shown in the last twenty years.
That's all there is to it, and that's why most people here are not particularly keen on accepting the idea.
