This is what I mean by mitigations
You could definitely hide far players, but as soon as a player is near enough they could be seen, particularly when dealing with humans making unpredictable input, that player's model will need to be placed in the world before either of them are supposed to see each other because the game has no way of knowing what that unpredictable input might be.
You can't have every permutation of a given player model being obscured by every possible combination of angles of scenery as distinct models in the GPU memory, so something client side will need to do that slicing, so a player's obscured origin location will need to be known by the client. This could give a player seconds of time to react depending on their opponent's strategy
A few milliseconds is the only advantage a player needs at the top level of these games to shift the balance in a given contest. And given the prizes for some of these tournaments is multiple millions, there's definitely the motivation to go to these seemingly extreme lengths