About a month ago, I saw an article on "load management" in the NBA. The term was unfamiliar. To summarize, Michael Jordan usually played 82 games per season. LeBron James didn't, at least not the last couple years. The James method is winning, and not just in the NBA. I don't think the shift back to a 15-day Injured List for MLB pitchers will change much.
Players used to be afraid to go on the injured list. With one-year contracts, the looming possibility was to be phased out if his replacement played well. Wally Pipp, being replaced by Lou Gehrig, was the extreme case.