I wouldn't have drafted Saquon Barkley in the top 10 of a draft, but that doesn't mean I'd have considered him a bad pick at #15.
Leagues are won with later draft picks. A good example is JOrdan Mason. No RB has done better than he has this year. I'm glad that I had him on my bench already when McCaffrey's health status was clearer.
This season, in that league, I've lost Cooper Kupp, Isiah Pacheco, and Kenneth Walker (for 2 weeks.). My only loss was by .8 points in the week that both Kupp (second quarter) and Pacheco (4th quarter) were hurt. An injury only hurts during the week that it happens. After that, I agree, cover injuries and it's not a big deal.
One sure way to limit your opportunities to cover injuries is by wasting roster spots. If you're in a 1 QB league, don't spend 2 rosters spots on QBs outside of a bye week. Unless you have a second TE who is flex worthy, don't waste a roster spot on a second TE. Don't waste a second roster spot on a kicker. Dont' waste a second roster spot on a D/ST.
When someone chooses to hold a second D/ST over covering up an injury to a running back, he chooses a losing strategy.