I've had two myself. it's not a muscle tear, it's a structural issue in the knee and once repaired there isn't an issue. People were way overhyping him before the injury and claiming the injuries took away athletic ability that was never there. He wasn't fast before the injuries. I think it's wildly ridiculous to claim he was great before he played a down and say that the only reason he isn't great now is because of injuries. Orthopedic surgery has come a long ways since Gayle Sayers, shoot it's come a long ways since I had mine reconstructed.
You are right every injury is different, but I didn't see a very different athlete before or after the injuries. He is what he is.