There's nothing any UniversalBlue image tweaks that you couldn't tweak yourself. It's just adding/removing packages, adding/removing drivers, a few configuration scripts, and a bunch of tweaks to fix well-known gaming-related issues.

But the point is that, if you want to game on Linux, you probably want to perform exactly or almost exactly the same tweaks that Bazzite already does. So why bother doing them yourself?

It's not even a linux-from-scratch situation where you'd do it for the sake of learning. Googling "my controller doesn't work right", finding some discussion threads, and copy-pasting a bunch of fixes isn't particularly interesting.