Not sure what Sonic you played, but Sonic 1, 2, 3, and Sonic & Knuckles were widely heralded for their smoothness when they came out on Genesis in the early ‘90s.
In all honesty sonic movement is pretty good, my take is exaggerated in order to compare it to mario, a game,I feel, that plays and flows slightly better than sonic(a surprisingly slow game despite the main characters name). That being said, younger me played the hell out of both of them.
Might be noticing key frame animation in 8 bit games. It can have a really nice subtle effect.