This is the very thing I've been banging on about.
Unless you can use substitutions realistically, i.e. like how the manager actually uses 'em in a match - they don't serve any general purpose.
They can serve a particular purpose in certain drafts, as a means to make it more difficult for the managers, yes - but that's pure bamboozle, forcing the managers to make changes, hitting them with random obstacles, game style.
You should be able to draft a 14 man squad and use OGS the way he was actually used - as an impact sub. You don't throw him on because of some random "injury" but because you feel that he would cause trouble for your opponent's defenders after 60 or 70 or 80 minutes of football.
Presently, though, we clearly can't incorporate that sort of "realistic" substitution in the basic "match" model we use - and so, well, there we are.
Randomised injuries is not a bad idea at all - but the concept clearly isn't suited to any kind of draft. It comes down to the basic difference between a "fun" draft and a "serious" one, I think.