Relevancy filtering is more for network traffic optimization, it doesn't really help with cheating in most cases. In a FPS, for example, the actors the cheater most wants to know about are almost always also network relevant.
But taking a step back, for fast games (like an FPS), the latency requirements drive you to send semi-secret info to the client (like the positions of other players), and so that's where things start to break down. But the traffic in the other direction is a problem too, as you have all of the scenarios in which the messages to the server (e.g. aim info, timing of weapon of firing) can be spoofed or engineered.
The motivation for the client-side anti-cheat systems is to extend as far as possible the envelope of what is considered trustworthy - i.e. if they can't solve the latency problem, then they try to make the client more trusted.
It's impossible to completely solve the problem, so it's about finding a solution that solves as much of the problem as possible. Unfortunately the main thing going for kernel anti-cheat is that most users don't care that they have to let someone root their machines to play a game, though the tide would likely turn if there were a high publicity exploit.
But taking a step back, for fast games (like an FPS), the latency requirements drive you to send semi-secret info to the client (like the positions of other players), and so that's where things start to break down. But the traffic in the other direction is a problem too, as you have all of the scenarios in which the messages to the server (e.g. aim info, timing of weapon of firing) can be spoofed or engineered.
The motivation for the client-side anti-cheat systems is to extend as far as possible the envelope of what is considered trustworthy - i.e. if they can't solve the latency problem, then they try to make the client more trusted.
It's impossible to completely solve the problem, so it's about finding a solution that solves as much of the problem as possible. Unfortunately the main thing going for kernel anti-cheat is that most users don't care that they have to let someone root their machines to play a game, though the tide would likely turn if there were a high publicity exploit.