This is the main point about past greats having success in the modern game. When we are talking about the elite of the elite from any period, it’s not hard to imagine Hank Aaron playing travel ball his entire life and weight training like a modern professional athlete still having great success today.
It’s the run of the mill MLB player that is better now than they were 50 years ago. The sheer number of athletes in the world means the average player is better now, but the top player may not be appreciably better.