I was _so_ excited when Rocket League first came to Linux, but that was several years before Proton[1] was released.
But according to [2] the game runs really well on Linux via Proton. Personally, I don't see any problem using Proton to play the game on my Linux gaming-rig.
The concern is that Epic will add EAC and that Proton is going to cause you to get banned or they pull the game from Steam and move it to EGS which doesn't run on Linux, and likely never will. So the question becomes why should I put more effort into a game that's likely not going to be available to me in the very near future?
Epic acquired Kamu, makers of Easy Anti Cheat, for use in Fortnite. EAC is known to block Linux players using Proton, and there's decent odds Epic adds EAC to Rocket League.
Proton is pretty great, but there are hardware limitations. Im running a pretty old video card. I can run games like Deep Rock Galactic on Windows, but it wont work on Linux as Proton needs newer linux drivers, which don't support my card, in order to run that game.
Proton works great for single player games but isn't that great of an idea for multiplayer games. Their anti-cheat system could end up banning proton users. I believe this has happened to Destiny 2 and GTA:O players.