Uhh, no… It’s because that’s not how anything works. There’s so many flaws in your argument, but here’s just one: if an enemy player is really well camouflaged but technically visible, then they would be rendered on the client side, but a human player would have to be very observant to spot them and kill them.
A cheater can replace the enemy character’s texture so that, on their screen, the enemy’s camouflage is useless and the player can spot them with no effort.
From everything the server can see, the cheater’s gameplay is legit. They could just be really good at spotting enemy camouflage. Only by looking at the client side render output, you can spot the cheat.
Unless the server is actually rendering the game for each player (which, spoiler alert, isn’t the case), most cheats are not detectable nor preventable on the server side.
Correct me if I’m wrong, but those games didn’t track official player rankings. Which is perfectly fine, and doesn’t make a game any less competitive, but official rankings is a legitimate feature that some people gravitate towards.
To be extra clear: I’m mostly with you, I think every multiplayer game should at least offer the option of self-hosted servers, and I backed Stop Killing Games to force them to do so (after official servers shut down).
Though to be honest… My opinion on this topic isn’t worth much. As I said, I don’t play any competitive games. So it’s very likely I’m missing some important info in my perspective.