I was under the assumption TGH (Toughness) impacts injury duration, but the concept could be the same.
Injury Prone + high toughness means a lot of "out for some plays" or "could play through it with less effectiveness if you wanted" injuries. May not even be out that long.
Also, I think it's fine the INJ is modified by the role. I think of it as a player with a vulnerable body part. Guy could be rock solid...except on his knee. So his bum knee gets hurt, it could impair him, otherwise, he's a horse and you wonder why he got the label...until he takes a helmet to that bum knee and you see he's got glass knees.
I like the dynamic - if we can't get a HC style "body part HP" system, this is the next best thing, but then maybe I have an over-active imagination to be able to abstract this kind of thing. (Might have come from playing so many war games where 1 tank = 100 or something lol)