I feel like a weird amount of Sonic autists rate 3&K poorly as a form of contrarianism or just not engaging with the game properly.
3&K isn't just a series of individual levels held together by a story blurb in the manual, they aimed to make it one cohesive adventure with proper ups and downs throughout.
You were never meant to play these levels individually in order to master them in an arcada-like set up, by this point Sonic's already evolving into a game where each stage is a piece of a larger whole rather than something to be experienced in a vacuum and so the levels are paced accordingly - hell if you look at where the series went after this it might still be the furthest they've ever pushed this concept.
It's a game that feels way more fun and fulfilling to play front to back than Sonic 2, with its slap dash selection of levels and wonky back half, ever could.