Buu considers that Goku hasn't changed ever since then:
Goku shows being nervous smilling and tells Buu that he is using a little item which gives an enormous power-up:
Buu tells as of things he could've said, which means that Buu considers that Goku is acting as an idiot:
Old Kaioshin and...
Well, Vegeta had far less potential than Goku and he considers that Goku has an innate talent, so he can't step up to him. Also it could be talking about Vegeta's current limit rather than Vegeta's whole limit as saiyans doesn't have limits.
Chapter: 456 (DBZ 262), P4.3
Context: as Babidi takes control of Vegeta
Babidi: “While I’m at it, I’ll draw out his hidden power to beyond [his? its?] limits!”
@GreatSaiyaman123
I think characters were rewritten since then as Krillin couldn't tell how Buu's ki changed from Fat to Super only Piccolo and maybe Goku could notice.
Even then, nobody seems to be telling that Gohan is showing more power/had gotten stronger while fighting Dabura since then...
I can't make any sense of that if that Gohan could already fill half of Buu's meter.
For me, maybe 18 couldn't tell the nature of Vegeta's ki and that statement is in reference of that.
Some people use this statement to say that SSJ Majin Vegeta in the Anime was the greatest ki she ever felt and say that he was stronger than SSJ2 Gohan:
However, in my guess, I think she is talking about the evilness of the ki that Majin Vegeta have, but that she can't comprehend. What would...
And he is shown dominating him and taking things slight, while Vegeta is tense and nervous, so Cell is emitting a false portion of his power to everyone which only Krillin and Trunks could tell.
@GreatSaiyaman123
Thing is, that you're ignoring context, Goku can do this and that because he is constantly luring them and making them think a different power level he is actually using. Of course it'd be worthless, they have to resort to strategies to an opponent that they have to manage and...
Considering how DB works I say that it does, Majin Buu is too powerful for SSJ2 Goku & Majin Vegeta before powering up again, but Goku thinks they by teaming up they could win (without knowing his hax, of course).
Then there are concepts such as Fusion being more than the sum of its components.
@Spiral-Force
I don't think anyone is while debating with you for too long, you go for cheap and childish tactics every now and then. I don't have to level up, you have, if you really think the way you are I recommend you to read more often or something that excercise your mind, if not you're...
He's stronger than them separated, but he isn't stronger than all of them together.
Sharing energy is not just adding ki, but far more than that. Considering that Piccolo send flying 4th form Freeza with Gohan & Krillin's ki while them teaming up were useless and not even for a warm up.
Plus...