I try Proton a few times a year and the experience is almost always disappointing; I'm not even a hardcore gamer, so mostly playing 2-3 year old games which I'd expect good experience with. However, if they ramp up investment and actually make Proton viable for the majority of titles, this is very bad news for Microsoft / Windows.
Protondb[1], which collects user reports, says:
18,811 games reported
15,261 games work
which is about 81% - a bit more than a simple majority.