Minimize the possible advantage by not sending the client other players' positions until absolutely necessary (either the client can see the other player, or there's a movement the client could make that would reveal the other player before receiving the next packet), and eliminate the cheaters you can with server-side behavior analysis and regular less-invasive client-side anticheat.

Ultimately even games with kernel anticheat have cheating issues; at some point you have to accept that you cannot stop 100.0% of cheaters. The solution to someone making an aimbot using a physically separate device (reading monitor output, giving mouse input) cannot be to require keys to the player's house.