Johnny Cage is the ego that walks like a man.

He has technical skill and he works out hard. That shouldn't help much against literal superhuman soldiers or supernatural creatures who were born to fight.

Johnny's knows in himself that he is the best! "How could this cyborg killing machine beat me? I'm Johnny Cage!"

His ego is so huge, his attitude so bombastic that he has pushed himself past any kind of sane human limit!

I am not sure that relaxed, deadpan Karl Urban could pull that off.