[kaetemi]

Look up BF2. Cheat tools would just disable limits locally on ammo requests, vehicle requests, artillery strikes, and so on. Server didn't check anything. It had fancy anti-cheat tech. Which was bypassed by just writing and restoring executable memory changes faster than the anti cheat detected.

Things are certainly not always as professional as they appear to be.

Visibility test is definitely feasible against wallhacks, it's not that expensive.

Aimbot is an assist cheat, which technically does not violate the physical rules of the game, so you are right that it's more difficult to detect. One solution to detect this class of cheating is to record the player's movement, and rely on a combination of outlier scores and outlier movement behavior to detect abuse. It's not watertight, but neither are any of these client side anti-cheat detection schemes.