>>720426489
Even though I think the series never reached the heights of the classic games and the 3D games never quite got the gameplay design nailed down, you're 100% right. Sticking with 2D would've been the death of the franchise. Castlevania went 3D, it wasn't a massive hit, went back to 2D, relegated to handhelds, died. Mega Man went 3D, it bombed, went back to 2D, relegated to handhelds, died. Even Rayman, even with the newer 2D games being great it didn't do anything for the franchise's success moving forward.
The fact that Sega never did stop pushing Sonic in 3D is the only reason it's still around. Presumably they only did that because Sega seriously lacks any other big hit franchises. They don't have some Resident Evil or AssCreed to really justify killing Sonic. Even Nintendo doesn't bring out 2D Mario that much.