Actually, looking at the line, there's nothing specifically saying it's about strength at all. He's specifically saying that, after defeating Buu, Goku is obviously #1, and we've clearly seen before that he's referred to Goku as being #1 due to his drive to fight (the whole "he doesn't fight to win, but fights because he won't lose" comment and what spurs him on to be the best fighter.Your example isn't the same. There's TONS of doubts as to whether Krillin is stronger than Piccolo. Here Vegeta says there's no doubt that Goku is the best after Kid Buu's defeat. Vegeta doesn't even say it's directly causal. Kid Buu's destruction allowed Goku to be the best with no doubts. That's it. He doesn't say Goku is the best because he beat Kid Buu. He just says that after Kid Buu is defeated Goku is now the best. The simplest interpretation is that Kid Buu was the strongest. Goku was the next strongest or his equal. Then with no Kid Buu, Goku is the strongest now. No matter the interpretation Goku is the best once Kid Buu is out of the picture.
Besides, there's tons of doubts about Goku being stronger than Gohan or Gotenks when he himself flat out states that he and Vegeta can't win against a form of Buu that Gotenks was equal to and Gohan was stronger than, and that he fought evenly against a form of Buu that he outright indicated had a power drop from when he was previously Evil Buu.
No, that's one of the lines that talks about Buu in general, and not a specific form of Buu. It's saying that, when Gotenks and Gohan were unable to resolve the problem of Ma-jin Buu, the overall strongest opponent in the universe they had to face, he had to take care of it. Since neither Gotenks nor Gohan ever fought Pure Buu, it's not possible for Goku to have had them try to resolve the problem of fighting him, so it's obvious he's talking about Buu in general."Goku tried to have the next generation resolve this problem, but in the end he was the one who defeated Buu, the strongest in the universe"
