I feel that you have to take in to consideration that lower gameshape means more fouls which means even greater chance of injury.
i am not so convinced with that, when the full team have problems with that, the opponent won't use him as a matchup more then normal - and i am quite sure that this is the reason why better defense could help with fouls. I checked one day games of the nt who was one by a high margin(i thing thirty points), which are often games betwen small nations and Powerhouses of BB and they make nearly the same amount of fouls and i seems more depending on tactics the teams play(inside draws a lot more). Which is also a bit astonitment, because the weak team makes more TO and get less second chanches.
So I think the player would have about 4 times the chance of injury compared to a player that plays a normal amount of minutes per week.
i never saw a injury while making a foul, you normaly get them while drawing them. Why you should fouled more often during 1400 minutes when you have weaker gameshape?
One argument you could bring which reduces the difference, is that the 70minute guy, still get his minutes even when you have a blowout or 6 fouls - but the other guy get at least the same chanche to get the 70 minutes but he don't stops them so that he get in average still more minutes and will reach the target earlier. And even an inccrease in 50% of speed while Gaining Xp would make an huge difference.