Valorant and Edan.gg's defender [1] has the best fog of war system I've ever seen. CSGO has probably the worst; in fact, at one point, the game had NONE and sent player pos's to everyone at all times.
I completely agree, but there are a lot of server-side mitigations that haven't been nearly as explored as I'd hope.
Check out https://edan.gg/defender to see the comparison between CSGO and a better FoW system.
Your cheat couldn't see those players because the server was doing a very cheap and primitive visibility calculation, deciding the player entities are dormant for you, and choosing to not send you the data for them.
This is different from the later-enabled player PVS system, which does more expensive ray casting once you get a certain distance away, which cut down on wallhack cheats a lot more [although they are still very useful]
Would an anticheat work if you did the opposite of this? Send the client random movement data above and behind them and if they spin and shoot towards it instant permaban forever
Random wonder. I have no idea in or around anticheating, please do feel free to shred it as an idea to pieces