The underlying coding behind staff members' influence in this game seems to be sound. For the past several seasons, I've gone for at least a superior level doctor, coupled with the taping injuries, specialty.
I've only had a player out once for more than a week, and that particular circumstance was only for two weeks, total, since I've made that decision. In the majority of injury scenarios that I've witnessed, for my squad, I've noticed a player is only out for that one, applicable, game.
Considering the affordability of acquiring new doctors, I haven't ever regretted making this choice. Now, if only trainers were so affordable..