Client still needs to know coordinates of opponents and other objects that could be in their view within the next 200ms, and once the client knows those, a cheating client can reveal opponent positions. You can't enforce that server side without adding huge mandatory lag to all clients.

But you can detect serverside (at least probabilistically) if a user is abusing it to their advantage.

Some Valve guy gave a great talk about their cheating detection a while back; I found it incredibly impressive: https://youtu.be/ObhK8lUfIlc (can't comment on their effectiveness these days, haven't played CS in a long time)