The glorification of athletes of prior eras is unfounded. What in the world makes you think the players back then cared more about winning championships than players now?
What I do know is that 90% of today's players work harder and are more dedicated to their craft than 90% of yesteryear's players.
Well, players played with broken legs, willingly amputated appendages, etc. to continue playing. So, there was a pretty high level of caring and dedication to team that you haven't seen in decades.
Also, those guys weren't making enough that they were rich. They still worked other jobs in the offseason. So, they didn't have the time or the facilities of today's athletes to train during the offseason.
The reason people are bigger, faster, stronger and better at the game is because they start earlier, are given more & better opportunities and everything is available to help them achieve the goals. (nutrition, specialized training & coaches, technology, etc.,)
No doubt a lot of these guys put in the time to look the part but its also easy for today's player to project an image that he is working really hard whether he is or not. Most of them care more about how they look than how they perform. So, just cause you hitting the gym doesn't mean you are becoming a better player.