I'd have to agree with Robert that Ruth, in his earlier years, had power hitting skills that were head and shoulders above anyone in the game. In the negro leagues, Josh Gibson was also dominant in that category.
Sugar Ray Robinson was very close to being undefeated in the 40's and 50's. He started out 40-0, lost to Jake LaMotta, then proceeded to go 88-0 after that (I will admit I had to look that up
).