I’m ok with that for things where I don’t care that much about how it looks (do I give a shit if I lose just a little detail on Happy Gilmore? Probably not) and agree that faking the grain probably gets you a closer look to the original if you’re gonna erase the grain for better compression, but if I want actual high quality for a film source then faked grain is no good, since if you’re having to fake it you definitely already sacrificed a lot of picture quality (because, again, the grain is the picture, you only get rid of it by discarding information from the picture)
But for anything modern, the film grain was likely added during post-production. So it really is just random noise, and there’s no reason it can’t be recreated (much more efficiently) on the client-side.