I disagree with the notion that it's better for the cheaters to have an easier time (and less chance of being detected), but you're right, BattleEye doesn't solve the cheating problem for GTA.

Rockstar should fix their netcode and run game server on dedicated server, instead of their customers PC's. I'd think decting aimbot isn't the biggest issue, while cheaters are able to break entire lobbies...

IMO no game should require client side anti cheat except for shooters, where looking through walls and aimbot is actually difficult to detect server side. At least for those is it possible to find valid arguments (except for being lazy).