I cannot speak to how many people cheat, because I have no idea.
However, I did want to share that I only started racing on zwift a couple weeks ago, and picked up several wins, and no cheating. So what that tells me, is either the cheaters all operate in higher levels, or, they aren’t really impacting the game.
I just happened to land at the very top of Cat C (fun is over today, I’v been bumped to Cat B). But if you are just borderline at the top of your Category, I think that’s where you need to be. If you cat down by exaggerating your weight, well…gee, you could in real life actually put weight on your bike…anyway< I think pride does prevent people from sandbagging. probably all cheating is with falsely low weights.