No, because 2D fans get a full game to themselves.

I've just listed 6 totally 3D games. You aren't taking in the information for some reason. This shouldn't be hard to understand either.

it's unfair to the 3D fans that they get only half a game

It's not unfair. Prior to forces and Mania they have received 6 totally 3D games versus 0 2D games. Adding Forces and Mania that makes the score 6 to 3D and 1.5 to 2D. That isn't a bias towards 2D. Do the the maths.

After colors was largely in 2D

The Sonic Colors I played was largely in 3D.

you're saying the 3D fans are spoiled?

Well there I'm playing with your logic. My honest opinion is that neither fanbase is spoiled and it seems a slightly silly thing to even debate. To me it boils down simply to there are roughly 2 groups of fans. 3D fans and 2D fans. Sega are trying to cater for both. Equally if I were to hazard a guess as to why Classic Sonic is back, I'd wager it's because he sells games. I don't think it's a coincidence that most of the the best reviewed Sonic games by a country mile involve classic.