I LOVE Shelton Benjamin and have been rooting for him in NJPW's G1 Climax that has been going on the last couple weeks. With that said:

He was never going to be the draw that Brock Lesnar is/was. Lesnar is a legit shoot fighting badass that walked into UFC with little MMA experience and took out the Heavyweight Division in an instant. He's not an all time great in MMA but the fact that he could win the UFC Heavyweight Title just goes to show that he's a bad ass. He looks like a vanilla gorilla and is a freakish athlete. Shelton is also a freakish athlete but not in the way that someone looks at him and goes "WOW THAT GUY IS ONE OF THE TOUGHEST IN THE WORLD".

Shelton is also held back by his lack of promo ability. Brock is better than him there and that's saying a lot because Brock is below average at best.

Shelton could have been handled better but he definitely had his limitations. They tried to give Bobby Lashley the same push that they gave Brock, he just didn't put asses in the seats like Brock did. In fact, WWE would love a top black guy, I just can't think of any in the industry that make sense as a headliner. Mark Henry is broken down and he's still pushed like a headliner. Maybe Big E can get there but he's still pretty green.

Roman Reigns is Samoan and is getting the biggest push in the company. They used Eddie and Guerrero to bring in the latino demographic for years. They're both talented but being Mexican probably helped them just like it helped Del Rio at first. Del Rio, like Shelton, was limited by his ability to speak on the mic.