I'd honestly rather have nothing in that place and Sonic Team strictly focused on making a game with polished Boost gameplay. Botched Classic Sonic gameplay is bad for its own reasons and genre roulette playstyles are also bad for their own reasons.
This doesn't have to be a Sophie's Choice.
I wouldn't mind it, but then you have to convince Sonic Team they can do a full game that can be sold for $60 or whatever featuring just boost gameplay and not have it be expensive as hell and/or 2 hours long. We all know the reason these things exist, and if they have to exist, which apparently they do, then it might as well be something that's fun even if not really THE GREATEST EVER. Because I find Generations' Classic levels fun, even if the levels aren't S3&K-like or whatever.
That said though, I do think people are sorta mean to Classic Sonic in Generations. It's not
botched. Sonic 4 is botched. Generations Sonic is simply different. The stages aren't designed to be like the Genesis' ones, and that's fine. The gameplay in there holds up well enough for them to be enjoyable and a different take on existing levels. I loved Rooftop Run Classic, for instance, and I'm glad it exists. Same could be said about Crisis City Classic. In general, even if they're not expansive like the old games, the stages have enough gimmicks for them to be interesting to go through and not feel like a chore.
But basically, at the end of the day, It doesn't have to be, but then it sorta does have to be Sophie's Choice. Which is the tough spot Sonic itself as a character exists. So, yarr.
Oh, and you know what's really terrible? Sonic Generations 3DS. Now that's a game I want to burn. Was it Dimps? I'm willing to bet it was, because they took the page from the stupid death pits right off Sonic Advance 2 and continued to copy/paste it every damn where. It's absolutely ridiculous how anyone could design 90% of those bottomless pits and think they're OK when stuff is thrown randomly after rails and you have no idea where you'll stop after jumping off from them, only to discover that you shouldn't actually be trying to go too fast or you'll fall down a place with nothing at all for no reason other to offer cheap deaths to the player. Now that's a crap Sonic game that actively manages to piss me off.