Well first of all what you say doesn't make sense. If Vince McMahon has the iron fist of approval before anything goes on air, then yes he is to blame for what we see, it has nothing to do with HHH, no matter what his job title is.
What I think happens he might come up with an idea, and then Vince will either do one of three things. He'll tweak it, say no, or let it go as planned. By the way I thing options 1 and 2 are probably what happens.
So yes HHH has a job mostly as an on air personality these days, because I do believe that Vince McMahon is a control freak. Vince will put out what he wants, and damm everyone who stands up against him, even his own son-in-law.
HHH has done a wonderful job with NXT, just look at the ratings for the show and the responses to the PPV's and live shows. I don't think taking over the main show will bite him in the ass at all. We might all benefit as fans because we'll get a better product as a result of it. It won't happen overnight, but we will see changes right away.
The big difference between HHH and Vince is that HHH isn't afraid to take a risk, he's young enough and he's in touch with the fans. If you look at NXT he gives them what they want, good wrestling, simple story lines and an entertaining show. Vince on the other hand is out of touch, seems set in his ways, won't change and the product is the worse off for it. So are we the fans who suffer through it on a weekly basis.