There's no point in nerfing Thanatos. In higher level play and especially in the pro leagues, Thanatos is one of the lowest tier junglers. The entire point of Thanatos is to win before the enemy team reaches lategame. If they do reach lategame, consider it a 4v5 because all your thanatos can do is ult and feed in teamfights. The best way to counter a thanatos is to just not die. It sounds stupid, yeah, but if you play safe and buy that aegis to counter his ult and starve him of kills he will never come online. A Thanatos that falls behind early game is a lost cause and an assured victory for the other team (assuming they are at least somewhat competent).