That's not true. They don't send data in _regions_ your client can't see/hear, but if an enemy is for example close to a corner or on the other side of a door, you can have a wallhack see that as the client is still receiving it.
Thanks to latency & the realities of the internet, the server has to bias towards sending data the client can't strictly see/hear at that exact moment, but potentially _could_ see if they move. Which is enough to give a wallhacker a meaningful advantage still.
But what you can't do anymore is see where all the enemies are going at the start of the round and run to the weaker part of the map or whatever. So reduced effectiveness, but still a thing.
Thanks to latency & the realities of the internet, the server has to bias towards sending data the client can't strictly see/hear at that exact moment, but potentially _could_ see if they move. Which is enough to give a wallhacker a meaningful advantage still.
But what you can't do anymore is see where all the enemies are going at the start of the round and run to the weaker part of the map or whatever. So reduced effectiveness, but still a thing.