No one is going to dethrone Cena as the face of the company, until he says he quits, that's just how it is. I accepted and realized this, a long time ago. AJ doesn't need to be the face of the company to be notice, heck I don't even considered him the face of TNA, I think Sting and Hardy gets a better reaction from the crowd than AJ does. He needs to showcase what he can do in "big leagues", like you said, he needs the exposure that he deserves.
I don't really understand, what you mean by watered down AJ, he a Christian so he doesn't really fit in with what TNA brings, whereas the WWE is more PGish, so the values is there. Or do you mean his movesets? The only real move he wouldn't be able to do is his Spiral tap finisher, which he hasn't done in years. Most of his moveset are safe if he doesn't botches it and he's no Sin Cara.