#3 Sami Callihan
Not every wrestler has to be someone who never stepped foot in a WWE ring. Sami Callihan stands out from the other people of this article because he did perform in a WWE ring and failed.
Known as Solomone Crowe in NXT, he was not able to reach the heights he could due to arriving at the time when NXT already had top stars in Sami Zayn, Kevin Owens, Neville, Baron Corbin, Samoa Joe, Hideo Itami, and Finn Balor. It also doesn't help the fact that the 'hacker' gimmick did not suit Callihan at all
After leaving WWE, Sami Callihan proved to the company that they dropped the ball with him. Right now, Callihan is one of the most hated heels of professional wrestling besides Tommaso Ciampa and Jay White.
He is a top star of Impact Wrestling (which is getting better now) and he had one of the greatest Impact feuds with Eddie Edwards.
Despite this, if Callihan returns to WWE NXT, he would once again be under-utilized. His foul-mouthed psychopath persona is not suited for WWE's PG environment.
He wouldn't be as violent as we know him to be should he sign with the company. Sami Callihan is a great wrestler, but the things that make him special and unique is not something we can see in WWE because that wouldn't be marketable.