red bikes are faster.

You don't need a chainstay bridge at all, and there are plenty of bikes that don't have a brake bridge. I always figured that brake bridges would help with blows from the side though. I have thought about leaving the chainstay bridge off, but I like to be able to mount fenders. You could add a mount, but then it might as well be a bridge.

I think the idea that you don't need a chainstay bridge didn't occur to anyone until the '80s or '90s. It seems that I've heard the bridge caused problems with super-light tubing, but the super-light tubing from back then is pretty normal today.