Boo grew so arrogant & overconfident because this was the greatest power he ever had though. Every single time that someone grew arrogant & overconfident was because of that. Why would Gotenks become so arrogant if he is weaker than he was before?
Why are you suggesting that Gotenks "powered up" in any way? That's the first time the boys ever fused correctly. I don't think Goten and Trunks are conscious inside Gotenks since Gotenks is a whole seperate being. When they defuse though, they are aware of what happened during the time they were together, but that's pretty much it. Also, when he first appears, he acts like Buu is nothing to him in his base form, even though the kids already knew how strong Buu was when he fought with Super Saiyan 2 Vegeta and then Super Saiyan 3 Goku.
More than x50. Is there anything that contradicts this?
Something like that. Where is the issue? Goku was no match for Evil Boo to begin with.
In rich respect, nothing. So if I may ask, where's the issue in my numbers? I placed my numbers where the plot needs them, and didn't look into small details such as, "Piccolo didn't stop them, so that must mean Gotenks is stronger," even if that scene solely just for plot build-up to begin with. I just have a tenancy to not make things "overly-bloated" when it comes to powers just so it makes the numbers more comparable. Unless comparisons in power are either plainly stated (while at the same time work within the sequence of events) or just blatantly obvious, I don't really care about
tiny details in the script when they don't really mean anything, despite other people thinking that they do. I just like the character's powers where they "need" to be, and as long as the events in the plot aren't contradicted, I'm fine with that. So as long as those powers suit the plot, preference is really subjective when it comes to power levels after Freeza.
Goten & Trunks are nearly equals, while Kibito & Kaioshin have a huge gap between them, so the boost shouldn't be extremely big.
Says who? In the potara fusion, they don't have to be equals. Plus Old Kai outright says that the potara is better than the fusion dance. If Kibito and Kaioshin did the fusion dance though, then I would agree.
Toriyama was planning to keep Goku dead, and keep Gohan as the main character who would kill Boo, so yes, I expect the main character (Gohan) to get this much stronger than the old main character (Goku) whom Toriyama decided to bring back at the last minute. Plus, Toriyama most likely wasn't using numbers, so all he had in his mind was "Evil Boo is much stronger than Fat Boo, SS Gotenks is much stronger than SS3 Goku, and SS3 Gotenks & U. Gohan are even stronger than that". Which is perfectly fine, because Goku or Pure Boo never fight with Gotenks, Gohan, or any form of Evil Boo, but we know that SS3 Goku with help from SS2 Vegeta stands no chance against Evil Boo. Besides, there is also base Vegetto, who is implied to be stronger than Gotenks Boo, and then he got x50 stronger, with potential to get x2, and possibly x4 on to of that stronger... Even in previous arcs, compare Chaozu with Oozaru Vegeta, or Kuririn with 1st Form Freeza, not to mention Full Power Freeza, or Kuririn with base Goku, or SS Goku, or SS Vegeta (pre) with #16, or SS Goku (post) with Super Perfect Cell... it's not the first time we see huge gaps when measured with numbers, it's just that the Boo arc is even more crazy, and this isn't the only thing that is crazy in the Boo arc.
Hm..you make some good points, but here's some things also:
1.Toriyama never suggested nor stated that Super Saiyan Gotenks is greater than Super Saiyan 3 Goku. Heck, the Daizenshuu 7 implies that until he hit the ROSAT, he didn't even surpass Super Saiyan 2 Vegeta. And from what I've seen in the manga, nothing contradicts that. Both Base Gotenks and Super Saiyan Gotenks lost outright to Buu, so there's not really any feats to go off of until he goes Super Saiyan 3 and actually holds an advantage.
2. The only thing Base Vegetto did was transform to Super Vegetto. That's it. I don't see how non-existent feats imply that his Base was greater than or on par with Buutenks.
3. Yes, the Buu arc is crazy and yes, Gohan was supposed to take the spotlight, but that doesn't mean Toriyama would completely debunk Goku and make him over hundreds of times weaker. It just doesn't really make sense in a writing viewpoint to COMPLETELY debunk the old main character. And making Gohan the main character was just his original idea of the ending, meaning he then had to change the ending in order to make Goku the hero again, but not when he was halfway done with the manga and then suddenly desides to change it. So why would he overpower all these characters, and especially forms of Buu, to around 200x-500x Super Saiyan 3 Goku, only to then degrade Buu's level back down to fit Goku's level? Plus, we don't know how much stronger Gohan is than Super Saiyan 3 Goku. All we know is that he's A LOT stronger. Whether it be 3.75x stronger

or 200x stronger, it really doesn't matter because the end result is the same. It just seems a little far-fetched to place them
that much stronger than Goku for no good reason is all.
He didn't mention that part in this statement
Yeah he did. At the beginning of this question which was right after the other questions about the heroes "raising their levels".
- The concept of fusion is also a form of leveling up. How did that concept come to be?
If I remember correctly, I was talking about how, as a concept, “there’s nothing stronger than a Super Saiyan”