It makes a lot of sense that it sadly is that way. Most of the linux gaming work does go into the compatibility layers and then the drivers and software stack is overwhelmingly tested on those compatibility layers due to the lack of demanding native games.
Another issue is that a lot of linux ports are from the original Steam Machine wave that haven’t been updated since. On Steam Deck it’ll automatically use the Proton version in these cases but I don’t think it applies to desktop.
Small tip: press the (i) on the right, next to game settings, and it’ll show what runtime is being used for this game at the bottom.
All they have to do is launch the next Pokémon on Steam and it’s all theirs again. :')