Debian is community run, which often means all changes and features get implemented because the community wants that, not some corporation. One notable example of that is Snap.
Also, I found (minimal install) Debian a bit more minimalist than Ubuntu server, which is great imo. I just want the bare minimum for my services to work, and pretty much the only thing I expect from my server to have is SSH and Docker.
Proton is just the compatibility layer, which allows you to play Windows games on Linux.
It’s one of the main reasons so many people switched to Linux in the last months and years, since Proton gets even better from week to week. Something, games designed for Windows run even better on Linux (Proton) than on Windows!
From what I’ve heard, requiring Proton isn’t that bad, especially for the devs. Often, games engineered for Windows run better on Linux than the same ones for Linux.