Josh had a bad gp season to but he was expected to podium too, so it's not like this is just a Mirai thing either.
Huge differences. Joshua was injured. That was why he had withdrawn from CoC (I am retrospectively glad; with his bad luck you just know it would have been HIM involved in the collision), and that was why his performance was so poor at NHK - and even then it was obvious that the two programs were special. Joshua also has an impeccable jump technique, almost never gets < (and only on the 4T nowadays, and then only rarely), and had a fairly solid competitive record until that point.
Whereas Mirai has continued poor technique on her jumps, was not injured, her protocols are littered with < and <<, and her competitive record is spotty at best.
Chalk and cheese.