It does become basically impossible if there aren’t strict limits on the art and level though(i.e ensuring walls or other blockers do not have small openings in them). Especially if you also want to use bushes as a thing to normally block sight as well. Though even then it’s still less effective then people think as you still need to replicate players not yet visible but could be if the local player moved a bit.

Let’s also not forget that you still need to deal with replicating things such as footsteps sounds through walls. Even if you replicate those as individual sound events instead of part of a replicated character that still gives a cheater enough information to know someone is there.