Vince Young could have been a very good QB, he just didn't want to be. People forget he had a good rookie season, won ROY and got a Pro Bowl election. Then at the end of his first season he had that whole statement about not liking the NFL and saying it was not as fun as it used to be. That right there tells you all you need to know about Young, he was gifted and coasted by on it during his entire amateur career, but when he got to the pros and needed to put in tons of work and dedication he couldn't cut it.
Johnny may be a great athlete, but he does no have near the natural gifts that Young did and he has had to work hard for everything he has gotten going all the way back to his freshman year in high school.