I agree about his ceiling. I don't agree that he has actual medical asthma. Hardy is indeed an A level athlete, and in his case it means he is built to sprint for 15 seconds and then rest and recover for multiple minutes. The actual amount of play time in an average NFL game is only 11 minutes, spread out over 3 plus hours. In addition he spent years training his "A level" body to be good at certain skills, most of which don't translate to MMA or at best have minimal application. Now he has to work on a much more diverse set of movements, and that takes time to get good because your body has to adapt.
Ultimately I don't see Hardy being anywhere close to a top guy in any combat sport. He can stomp some guys in the sub-top 10/15, but I don't see him rising above that.