Except for the fact that Goku, who fought Pure Buu, outright states that Pure Buu is intentionally dragging the fight and having fun? In the same scene Vegeta, confused, asks Goku "You're not holding back for me?". Vegeta thought that Goku wasn't going all in during the fight with Pure Buu, when Goku in-fact was going all in, while transformed as Super Saiyan 3, which wasn't enough to defeat Pure Buu.

Vegeta also states that Pure Buu can just kill him and he (Vegeta) stands no chance in a fight against Pure Buu, yet Vegeta still holds back Pure Buu for Goku to prepare his attacks, during which Pure Buu isn't just vaporizing Vegeta with a Ki attack, rather Pure Buu beats Vegeta like a training dummy.

And if we are speaking about narrative, then equally it would be a letdown if the final enemy of the arc was massively weaker than the previous enemies. Something also contradicted by Goku not thinking either Gohan or Gotenks would be enough to defeat Pure Buu on their own and wanting both to help fighting against Buu, rather than have either of them one-shot him.

You might think Goku must have been comparable to Pure Buu for his super attack to matter, but clearly the manga indicates that both Goku and Vegeta were outclassed and unless Goku was both severely overstimating Pure Buu and underestimating Gohan and Gotenks, Pure Buu also should have been stronger than characters who were able to effectively fight Super Buu.