Sonic & Knuckles really carries S3&K's reputation imo. The level layouts are just better, the bosses are cooler, the alternate Knuckles paths add replayability... Sonic 3 alone is just so lacking in comparison. It's much more unfair, there feels like more random crushing and bottomless/spike pits, not to mention the Barrel of Doom and other poorly explained gimmicks... I know that the fandom convention is to talk about these games as one, but I think there are real differences between them and its kinda obvious even just playing through S3&K start to finish how much more polished the S&K half is. Idk it could be productive to dig into those differences and see if there's anything to learn or uncover.