Brock never could talk either but he quickly won Randy Orton never had the best promos either.
Difference to me is that Shelton never had a character... like at all.
I don't think it's by chance that the only time he really ever got heat as a heel was when he had "Mama" with him. I know some of us didn't care for that, but she def. got him booed and he played the Mama's boy role well. It got heat for those couple months they were running it before Thea got sick. Outside of that, he's always been dope in the ring, but plain. With Lesnar, he's a big, intense, overly aggressive MF who looked like he could kill you. Orton isn't an outstanding promo but he had a character as an disrespectful, arrogant, borderline psychotic dude. Shelton was... Shelton Benjamin.