I don't know who the greatest baseball hitter is, but he almost certainly played in the last 40 years, 50 years at the most. Players today are bigger, stronger, and better conditioned now than they were before the 1960's. Babe Ruth was a behemoth in his day, but he weighted 198 pounds in his prime which is puny by today's standards.
But when judged against his peers, there is little doubt that Babe Ruth was the greatest baseball player of all time. Ruth not only set homerun records that held for decades after starting his career as a pitcher in the deadball era, but he out-homered whole teams a couple of seasons.