Anyone saying KP has always been just around peak human is objectively wrong. It isn't just that he overpowered Spider-Man on several occasions (holding back is one thing, getting your sh*t rocked in strength is quite another), but he had numerous other feats that don't involve such subjectivity. Among other things, he snapped steel beams with his bare hands, and toppled a structure that was easily multiple tons in weight. Classic was written as at least Class 10.
He's not there now, and there was no stated depowering. It just happened due to writer portrayal. Welcome to comics.
Anyway, Classic KP destroys Beast.