I think you're giving me too much credit. I'm not arguing that football is less debilitating for its players than MMA, and that's why I draw my line between the two sports. The difference for me is purely aesthetic.
Similarly, I would happily shoot a majestic elk in the face if I was going to turn it into delicious charcuterie later, but I wouldn't shoot a rhinoceros for sport if there were a billion of them. It's not about the animal, or the suffering it endures; it's entirely about the form of entertainment I'm getting out of it. I'd justify doing just about anything for food, but killing purely for pleasure strikes me as sadistic.
And please don't think that I'm judging anyone for enjoying MMA. If you find a nobility and an honor in it, then I'd say it's moral for you to enjoy it. For me it would be immoral, not because my standards are higher than yours, but because it looks like a human cockfight to me.