The only thing you can do is compare a player to his contemporaries. And clearly Ruth was the most dominant player of an era. Of course advances in technology, nutrition, training, etc. make today’s ballplayers much better than the players of a hundred years ago, in absolute terms, but greatness is something that is measured relatively.
Ruth would play in the Regular Season, then he would go out and Barnstirm against black players. They said he was the toughest they ever played against. His Carrer war is 183.5.