I'm not as mad at Epic as you are, but sure, they can eat several bags of dicks, whatever. However, factually, whether they are or aren't all in on Linux remains to be seen. I won't make a prediction but I will say that I think it makes sense for them to embrace it now for all the same reasons it makes sense for Valve to continue to do so. Valve paved the way and did the hard work, and Epic would like to come from behind and be a solid #2.
To that I say, bring it on. Even if they are only interested in selling me shit, the more big money-slinging companies back Linux, the better. All the games I ever got from Epic were part of a Humble Bundle or free as in beer, and so far all of them will run fine on Linux. But then, IDGAF about Fortnite. The game I want to have working DRM on Linux is Rust, but I wouldn't accept kernel DRM to get that.
The real question, not for me or you but among populations which matter, is going to be how odious the DRM requirement for Fortnite is.
As for Epic being dependent on Proton, Proton is dependent on Wine, it's all a big dependency party and it's how things are supposed to work. Who knows, maybe they will become significant contributors.