6. Samoa Joe
If there's a criticism to be made of Samoa Joe's WWE run, it's that he's been too often portrayed as a man and not the monster he truly is.
Fortunately, his heel turn and feud with AJ Styles seem to have alleviated that. Joe is capable of being fearsome and downright sinister on the microphone. So long as Joe believes in Joe, he is a nigh-unstoppable force both on the mic and in the ring.
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He was an early pioneer of mixing MMA influences into pro wrestling, and still trains heavily in that style, eschewing the more common bodybuilding techniques most wrestlers at least spend some time on.
Why he might be the top guy: Joe's been the top guy in TNA/Impact, and did a fine job so long as the company was behind him. He has the size, the presence, and the reputation to be the star of WWE programming.
Why he might not be the top guy after all: Joe is a monster, but he's a little slower and more cautious of a monster these days. His intensely physical style takes a toll both on himself and his opponent, so he may not have many years left to wrestle.