Yeah, anti-cheat support is probably the biggest barrier right now. The Steam Deck already showed that many gamers do not really care about the OS as long as their favorite games work smoothly.
I don't think you'd need to block multi tasking though, but the kernel would need to prevent or tamper root access so it couldn't modify the game memory.
Userland anti cheats can work (and do) on Linux if the developers want to. Most of the third party ones the developer buys/licenses already do.
But reality is that only the kernel level ones seem to work to some extent. Difference in the amount cheating between counter strike and valorant is just massive (both free to play games)
I'm sure there's a reason why they don't, but I wonder why games don't try implementing honey pots, like rendering a fake player behind a wall and automatically banning if a player's crosshair snaps onto them, etc.
In other words, no one is going to refuse to use Linux out of loyalty to Windows, as long as all the games they want to play work.