I game on linux regularly, primarily thanks to Valve. In the last 2 months steam lists 11 different games I’ve “Played Recently”.
7 worked flawlessly (Baldur’s Gate 3, Destroy All Humans!, Divinity: Original Sin 2, Besiege, Deep Rock Galactic, Shotgun King, Call of Cthulhu)
1 the native linux version doesn’t work, but the windows version works perfectly (Northgard)
1 didn’t initially work, but worked a month later after proton was updated. (Grounded)
1 I had to choose an older version of Proton (due to the external launcher breaking things), but with enough performance hitching during cutscenes that I chose to just play it on windows (Star Wars Jedi: Fallen Order)
1 I couldn’t get to work, but I honestly don’t know if it’s a linux issue because the game’s discussion forums are full of people saying the game is riddled with game breaking bugs on windows (The Sinking City)
I’ve been gaming on linux for a couple of years now, over that time I’ve put many hours into WoW, Sea of Thieves, Rimworld, Golf with your Friends, Core Keeper, Outer Wilds, and dozens more without any issues at all. 90%+ of the time the game starts up and just works.
I’m just one datapoint, but yeah, Linux as a gaming platform is totally viable for me these days.
Also, protondb lists 19% Verified and 16% Playable, so your 5% number is just demonstrably wrong.