I'm not the person you were talking with, but I mostly agree with them.

Here's the thing, client side anti-cheating is a losing battle, it's the equivalent of adding spikes to your key so you can give it to someone so they won't be able to open your door, once they have the key they can remove the spikes. Client side anti-cheat can ALWAYS be bypassed, they rely on security by obscurity to prevent people from removing the actual check, but it's a losing battle, no exceptions.

Server side anti-cheat is the only method that has the possibility of being accurate. Like you said, you can make your aim-bot be indistinguishable from human, but then you're going to be on a human level and other humans might beat you. Any game that worries about this already has a skill based matchmaking, which means that cheaters will end up playing with other cheaters or humans with a similar level of skill, so who cares?. You might get one cheater that's still ranking up on a match, but on the long run they'll cluster together.