This is the question that anti-cheat conveniently dodges.
The real problem is that "cheating" is practically undefinable. What players really need is moderation. There is no relevant difference, from a player's perspective, between playing against a cheater or playing against a legitimately skilled person. If someone is not fun to play with, then that needs to be managed somehow.
The most effective strategy is for players to moderate the servers they play on. This has recently become impossible, because game studios have chosen to monopolize server hosting while also abdicating the responsibility of moderation. Anti-cheat is nothing more than a lazy implementation of automated moderation.
There's a reason that Battlefield 4 is still going strong, while Battlefield One (which came out just after 4) is unplayable. That reason is player-hosted servers.
Moderation is a fine suggestion. This idea could actually be implemented in such a way that other player clients do detection and reporting behind the scenes. Suppose a ton of clients see one user violating rules of the physics engine. Automated reporting on that can be observed as a trend and a ban would make sense.
Having argued about this specific topic in the past, I agree that going so far as to do checks on player movement is difficult and even expensive if you're validating physics for every user.
What concerns me more is the increased risk of RCEs when developers skip fundamental security practices because "the anti-cheat handles it" for them.
This is the question that anti-cheat conveniently dodges.
The real problem is that "cheating" is practically undefinable. What players really need is moderation. There is no relevant difference, from a player's perspective, between playing against a cheater or playing against a legitimately skilled person. If someone is not fun to play with, then that needs to be managed somehow.
The most effective strategy is for players to moderate the servers they play on. This has recently become impossible, because game studios have chosen to monopolize server hosting while also abdicating the responsibility of moderation. Anti-cheat is nothing more than a lazy implementation of automated moderation.
There's a reason that Battlefield 4 is still going strong, while Battlefield One (which came out just after 4) is unplayable. That reason is player-hosted servers.