#5 Shelton Benjamin

This wrestler was doing things Kofi Kingston does before the faux-Jamaican was creating new ways to stave off eliminations in the Royal Rumble.
Benjamin is one of the most physically gifted Superstars WWE has ever had (watch any ladder match he's been in) but he's never been seen as more than a mid-card guy or a tag team specialist.
Did you know a top WWE Superstar just wrestled outside the company? More details HERE
He did have some good matches with Daniel Bryan and others upon his return to WWE, but he's been seen on SmackDown about as much as we've seen Bray Wyatt lately.
Like the Kanellis', he was resigned to help the brand split and to keep him from the competitors.
While he did have some success in NJPW and as a tag team with Charlie Haas in ROH, if he was released, he would probably experience the same type of booking prior to getting the call to come back to WWE.
He's still uber-talented but his release wouldn't sink the WWE. If they thought more of him then he'd be on TV or in more storylines.