MVP and Jericho are much better on the mic than Dibiase Jr. If they had turned Ted Jr. against Randy during the Legacy angle (it never got out of angle and became a real group) but they decided not to and that moment has passed. In this promo/skit heavy era, a face has to be as able on the mic as a heel. But you're definitely correct, it's all about what the writers give them. It also takes someone believing and pushing for them backstage.
I have to agree and disagree with you. You are right in that MVP and Jericho are better on the mic than Dibiase Jr. As a matter of fact,they're better on the mic than 99% of the other wrestlers out there. But with that said I think that it's more important to be good on the mic as a heel. I believe that that's one of the reasons why Shelton Benjamin never got completely over as a heel. He got over as a face with his athleticism and quality matches.And both Kofi and Daniel Bryan have as well. As a heel Dibiase has done nothing but brag that he's rich and take Maryse as his valet.No big promos and nothing much in the way of feuds either.
I still think Miz is gonna be the first one to fail at cashing that shit in. 
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Ya'll see that little white girl mean muggin like a muthafucka lol