This means...
...the fact that Goku and Vegeta even humored the idea of battling Kid Buu means that his Ki dropped after explicitly rising from a point that Goku considered impossible to confront, let alone defeat.
Kibito Kai even confirmed that, upon Good Buu being removed, Super Buu was reverting into his original form, cycling through his multiple different previous phases, including Buff Buu, which is the direct result of Buu absorbing the South Supreme Kai. With Good Buu removed from his body, the South Supreme Kai, the source behind Buff Buu's strength, is removed, too, which means Kid Buu is not as strong as Buff Buu.
Is not like Goku has never demonstrated the ability to inflict significant damage upon Kid Buu.
He has.
Twice, in fact.
The only reason "Even a full power Goku [failed to] defeat [Buu]" is because, by the time Vegeta even proposed the idea,
Goku needed an entire minute to build up the Ki required to pull off his end-all be-all attack, and when he
did nearly reach full power,
his Ki quickly began to wane,
to the point where he failed to even launch the Super Spirit Bomb properly.
There is no statement nor any evidence to support the claim that Super Buu after transforming and buffing up while rising is chi, gets lower after becoming kid buu. If it were the case,
they would have stated that his ki dropped , not that it
increased has it doesnt make anysense as it should have dropped the moment Super Buu lost Fat Buu going with your argument. Even if the good buu or south supreme kai (
and if that was also true for good buu than for sure, when he lost him, Kid Buu would have been fodder, and wouldn't require Ssj3 building up power to kill kid buu has the two saiyans would have know that he got "weaker"yet they never once comment upon him getting weaker from that . He wouldn't be able to deal with a genki dama comprised of genki from people such has ultimate gohan) were removed he was never stated to be weaker than when his chi was rising from buff buu to kid buu. In fact,
Super Buu himself states, he won't be himself if they take out good buu from him, he himself never stated he would be any weaker. And, if kid buu was somehow weaker, it doesn't make sense has to why , Kibito kai would
be sweating having a look of fear on his face for what it is to come, after kid buu's presence if somehow he his weaker than Super Buu. As even if he his the most troublesome, it wouldn't matter if he his significantly weaker and can therefor be delt easily.
Also, When Super Buu was formed by absorbing good buu,
piccolo states that his Ki changed and was better suited for battle but never states it got bigger.
This is supported when goku also senses Super Buu's ki but never states that it got stronger or increased despite the fact that this same goku
could sense the increase in ki of Fat Buu. Dabura also makes the point that, they cannot use the ki of gods like shin or kibito for majin buu to absorb it and
reach full power. This means, Kid Buu's ki could not have risen when he absorbed South and Dai Kaioshin (Super Buu and Fat Buu Respectively).
Dende In Super also makes a point that, Kid Buu, the ones that got reincarnated into Uub was the most formidable enemy Goku had to face, despite the existences of other Buu's such has Super Buu that he was there to see and witness. When the Kaioshins are taken away from Super Buu, his ki begins to increase instead of decreasing.
In a small bonus tangent in the anime, it's stated by Kibito Shin that through absorption (referring to kid buu) had allowed his power to even be reduced. Thus, that would prove and steelman my arguments and why his chi increased instead of decreasing, it would also support the argument of the kaioshin's ki not making him stronger when he absorbs that and why he would be equal or very likely stronger than Super Buu.
Them humoring the idea of beating Kid buu is their
own character flaw, it doesn't prove beyond a reasonable doubt that somehow Buff Buu got weaker or something. As they were blatantly incorrect and proven
wrong after they fought him.
It's no difference than Vegeta after seeing semi-perfect cell becoming perfect cell, still thinks he can easly beat him. Despite the fact that
Cell was suppressed, something
vegeta doesnt notice. By your logic and your argument, because vegeta thought he could also beat perfect cell, it must mean that when perfect cell transformed, his ki must have become weaker or not change at all for vegeta to make such claim that he can beat him before the fight starts. In a similar manner ,
kid buu was simply having fun when fighting ssj3 goku. He was so suppressed at one point that even
hercule could tank 1 punch from him. The reason they thought they could beat him was because kid buu doesn't look physically impressive vegeta called him "
little friend", not because his ki was weaker. I already went over this point above, were they often underestimate their opponents based only on their physical appearance.
I never said Goku has never demonstrated the ability to inflict significant damage upon Kid Buu. Inflicting relevant damage and outright beating and killing buu are two different concepts.
In that tangent base goku also did something similar to Buutenks.
Vegeta being able to blow off the lower part of Kid buu.
Mssj goku being able to blow off the upper body of perfect cell. Or v
egeta'S final flash doing relevant damage to perfect cell.
Even SSJ Gotenk was also able to do significant damage to Super Buu. Yet,
he needed ssj3 to not only reach the level of power of
Super Buu when he escaped the time chamber,
but also be able to finally get rid of him. The point being, it doesn't mean they are relative to their respective opponents in strength, unless you think ssg2 vegeta or mssj goku being both stronger than perfect cell. But obviously, the two feats you shown proves nothing has, it doesn't matter for Buu when he can
simply regenerate as
even regular bullets can pierce threw Super Buu's skin.
The Daizenshuu makes it clear that even if he was at full power, it wouldn't matter. Kid Buu, didn't even care what Goku did. Goku was standing still building up chi,
since kid buu would have logically retain the ability to sense ki just like super Buu he would have simply blitz vegeta and stop goku at any point he wanted if it was somehow a problem. T
he only time we see a worry on kid buu's face is when the genki dama is completed and goku uses it against kid buu.
