The 3b just has USB 2, so even with slow spinning rust, that’s going to be a bottleneck. But it’s probably still plenty fast as a remote storage device for media storage.
Edit: said I didn’t know OP’s use case but in re-reading they did say. Edited accordingly.
It’s my understanding that anti-cheat CAN work in Linux and does with some games. The point is still valid of course. If a specific game someone wants to play doesn’t work, that’s going to be a frustrating experience. But still I foresee the percentage of Linux gamers will continue to grow. And gaming companies increasingly making sure to use anti-cheat software that does work with Linux, as that market share is becoming too large to ignore.