I'm a programmer, yes it is. It's not easy in the sense of easy to implement, it's easy in the sense that everything else is impossible. Client-side anti-cheat is impossible, and by that I don't mean hard, I mean perpetual-motion level of impossibility. If someone tells you they implemented a foolproof client-side anti-cheat you should be just as skeptical as if someone tells you they created a perpetual motion. It's impossible, never going to happen, want an example? Robot using a camera to watch the screen and directly moving the mouse and keyboard, completely undetectable from the client side.

From the server perspective the person is cheating or is behaving like a human. If they're behaving like a human their behavior is completely indistinguishable from a human, so who cares if they're cheating?, whatever they're doing has them still at human level so if the game has skill based matchmaking (which most of these games do) he'll rise up until his cheating puts him in the same level of more skilled humans and everyone has fun. If he keeps rising forever he's not on a human level, therefore a cheater. More importantly this also penalizes people who buy bot leveled accounts, because their matches will be all against people they can't hope to win and the game will not be fun.

Server side can also trick clients into giving up that they're cheating, e.g. sending ghosts behind walls to check for wall hacks or other similar things to gauge player responses.

But what do I know? I'm just a senior programmer who's been working on servers for some years. l never worked on the client side anti-cheat though, also never tried to build a perpetual motion machine.