No, they haven't.
Guys used to pop amphetamines to recover from the game the night before and drink beers to come down from that night's game. Greenies were a bigger issue than steroids. I wouldn't classify that as proper nutrition and rehab.
I got my completely torn ACL reconstructed in 1995 (by a doctor in the same practice as the Red Sox team orthopedist, incidentally). I was in the hospital for 3 days and it took my over a year to feel pre-surgery comfortable again. Heck, I was barely able to walk without crutches when I stepped foot in Storrs, 3 weeks later. Today, it's more or less outpatient surgery, doesn't leave a 4 inch scar, and takes 3/4 the time to recover at a world class level.
More recently, I was diagnosed with a tear in my Achilles, as well as peroneal tendinitis. I couldn't walk without a limp and Advil was useless for the pain. I was prescribed shockwave therapy and physical therapy just like a pro athlete would (only difference is they would get it daily and wouldn't have to pay for it.). 2 months later the tear is healed and I can run with no more soreness than a typical 42 year old should have.
Obviously, those are personal and anecdotal, and I am not, nor ever was, a world class athlete. So be that as it may, check out this series of articles regarding the
history of strength training in baseball. It's not been around that long.