Again, the problem is SIZE. Elgin is a BEAST in ROH, but take him to WWE and he's suddenly middle of the pack. He's intimidating to guys like Richards who are under 6'0" but stand him to next to Ryback and its a joke.
He would basically be to WWE what Mike Mondo is to ROH, gimmick wise.
Bryan is an exceptional, exceptional case, and if he wasn't literally THE best in-ring worker in the world it might not have happened for him.
Kyle O'Reilly could flourish in the X-Division by bringing a different style and standing out, but I really struggle to see him reaching any higher.
Adam Cole I fully admit could be a megastar. The literal babyface, the outgoing personality, the athleticism, the awesome attitude--IF ROH can hold onto him they might strike gold, but that's a big if.
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Thank you, Eddie Guerrero.
http://www.wwe.com/f/styles/photo_large/public/photo/image/2012/04/33_Moscow_04112012jg_02128.jpg