I'll speak as a black fan that lost interest in the mid-2000s and didn't go back until CM Punk's rise:
Shelton, Lashley and MVP all bored the shyt out of me. I know you younger guys who grew up with them feel different but honestly every member of the Nation was more interesting than those guys, IMO. Shelton could go in the ring but had the personality of store-brand toilet paper, MVP never came off as larger than life the way he or WWE would have you believe, and Lashley was just stiff and unready.
Hell, I even like Kofi, but he was never gonna be a legit star doing that fake Jamaican shyt they had him doing. The ceiling on a gimmick like that is the IC title scene.
R-Truth has always been ridiculous. He wears airbrushed jeans. Stop.
Honestly, Mark Henry's Hall of Pain run is the only truly missed opportunity IMO. Going back and watching those promos and matches, Mark was a star and it's a shame it took WWE so long to stop putting one of their most truly intimidating talents in comedy angles with trannies and old ladies. Even when he was filming silly bits with Chyna and D-LO he always seemed like someone who would whoop some ass. He was more believable holding the Big Gold Belt in his hand than any of those other guys would have been and should've gotten the WWE title at least once. The only black star since Booker to actually seem believable as a threat against anyone on the roster.
As for current guys, Big E might be the closest but the comedy would need to be scaled back for some viciousness from time to time. The Rock had his silly shyt only after being a complete p.o.s. in the Nation so fans already thought of him as a dude who'll wreck shyt (got brought into the Nation and then jumped Farooq out his own gang, beat Foley within an inch of his life, etc.). Apollo and Jason Jordan ain't shown enough yet but both are a looooooong way away. That Crawford dude from NXT that's piping Binky looks like he might have a little late 90s-Rock swag but he's years away, too. Patrick Clark is never holding a major title as a Prince impersonator.
When it comes to this main event shyt, I just don't buy it from most guys. Never bought it from Del Rio, Swagger or Sheamus, so it's not a size thing either. Some people just have that star thing about them and even when you do, your look, your promos, your character all have to be perfect.