It was! The 8-bit SMS/Game Gear version was introduced in 1991.

Though it was not a port, rather a completely different game developed by a completely different team. It was a good game in its own right, but it’s not comparable to the 16 bit original.

Some people (like me) prefer the 8 bit Sonic games. Sonic 2 for Master System was a completely original game, and it is a 2D platforming gem.

I agree, and in fact Sonic 2 for SMS was my first foray into Sonic as a child. A great game. A brilliant game. But way too different to make useful comparisons to the 16 bit games.

And music (and production, I believe?) by Yuzo Koshiro. A legend.

Oh..so was it a port? Hadn't the genesis been introduced by then?

It was a demake[1], by a different developer, with totally different levels, simplified graphics and audio, and slightly different gameplay.

1: warning, tvtropes: https://tvtropes.org/pmwiki/pmwiki.php/Main/VideoGameDemake