As someone who has had a concussion before, I agree that getting a concussion is worse and likely has a more profound impact on your day to day life than a catastrophic knee injury. It's likely more painful and a harder injury to manage going forward through the rest of your life. I've been there; I've literally passed out in pain and vertigo from trying to do basic addition.
As awful as "rehabbing" w concussion is, it's a passive process that happens regardless of someone's will or dedication. Rest is the primary treatment for the acute symptoms of concussion, and there is no proof anything else even does as much as give a placebo effect. If you don't believe me, believe the scientific research;
Rehabilitation of Concussion and Post-concussion Syndrome
My experience rehabbing a concussion largely was just being high on pain killers and sleeping for a couple months until I could think properly. I wasn't pressing and pushing and willing, I had given up and was waiting to die. It sucked. A lot.
Compare to McDavid who did 10 hrs a day for 5 of months pushing himself and his body to the limit and not overstepping to make a 2 year recovery time 5 months. He lived and breathed being able to play on opening night all day every day all summer. You can't compare the two. Would I rather be rehabbing my knee than a concussion? Absolutely. If I was rehabbing my knee, could I do it like McDavid did? Probably not. But I certainly could and did rehab my concussion the exact same way Sidney Crosby, and even Johns did. And while getting back to the gym after all your muscles have decayed and weakened sucks, it's not the same as trying to get back through an injured muscle.
I think it makes sense for McDavid to win. He showed incredible will, fortitude, and dedication in his rehab process. He took a risk because of his love of the game, and refused to miss action. It's remarkable. The dude is basically not even human. I think McDavid should win the Masterton.