Server side is beatable as in, you could inflate your skill to that of a professional player.

The optimal serverside anti cheat would be able to recognize what gameplay is human level, and what gameplay is impossible or very unlikely to be human, and make punishment decisions based on that.

Then, the best cheat would just be almost perfectly simulating a pro player, and at that point the cat and mouse game of anti cheat and cheating would be far far less relevant.

Something like blatant tf2 spinbotting, or scoping someones head through a wall right before peeking them in r6, are absolutely detectable serverside with heuristics or machine learning models or etc, and that should be worked on rather than embedding some spyware into my uefi firmware or whatever.

go look at some forums for cheating, and you will see that they really do not work very well. it may be a cat and mouse game, but there is constant reverse engineering work and development being done (some of which is even paid work for paid cheats), and there is pretty much always a solution for new anticheat measures that someone finds.

the only unbeatable anticheat is a server side one

voting third party will just split the vote for the side you want though (and thats a big problem when the opponent is literal evil or whatever, and the margins are so tight), we need to switch to a better voting system like ranked choice voting to allow more than 2 options.