As a comparison, before proton, you could run steam with wine under linux. Wine directx implementation was sufficient to make a quite a few games work just fine, but the experience was atrocious. You either had to install a new instance of steam per game or install everything under one bottle which didn't work well as you had to tweak the install per grame. Personally I used it just for one or two of games that I really wanted to play and could actually run outsisde of steam after installation.

In comparison the proton experience is seamless.