Hard to compare across sports, but
Linebackers are bigger, faster, and hit much harder today. Walter Payton would still be great, but he would play as hard as any player in the current game.
Pitchers, on average, throw harder now than they did in Pete Rose's era. Pete Rose would still be great today, but I get the feeling Mike Trout would still be a better player if both were playing todays game
Between the mess he had made of the Bulls and the similar problems we are seeing with the Timberwolves, Tom Thibodeau coached teams are a stern warning of what happens when you don't rest basketball players
I guess what I'm trying to say is, sports medicine has gotten a lot better, but teams are also getting smarter. Better players, increased intensity, increased risk of injury. Teams have deemed resting players as a potential way to address these risk.