Injuries affect a team, for sure. But this is the difference between the way Bo has it and others had it: people will get hurt every year, get 2 or 3 deep, and there isn't much drop off; practice everyone hard and get everyone prepared, that way if someone goes down, the next guy is ready....OR practce soft, promise startng roles, dole out unearned depth charts, and practce nepotism, so that when someone gets hurt, no one is ready.
The next person will be ready, because they've been PRACTICING to be ready.