This is true of any online game ever. Games require integrity and there are plenty of people who would rather have game integrity than system integrity because, for them, the system is for the game.
I don’t think Riot is losing sleep over denying access to the 4 people who want to play Valorant on a Steam Deck.
And for macOS the OS itself provides enough system integrity that Riot don't need a kernel anticheat on macOS.
Steam Deck users need to ask Valve to similarly improve SteamOS's system integrity to prove to game companies that it's safe for people to run their games on it without compromising their game's integrity.
As a Steam Deck user I'd rather have the platform kept open like how it is now than lock it down. It's one of the significant advantages the Steam Deck (and PC gaming in general) has over consoles.
I don’t think Riot is losing sleep over denying access to the 4 people who want to play Valorant on a Steam Deck.