#4 Robert Roode

How could it go so wrong? Robert Roode is one of the most decorated performers in TNA Impact Wrestling history, he did it all in both singles and tag teaming. Roode would join WWE in 2016 and almost immediately became the top heel in NXT, which was soon followed by becoming NXT Champion and defeating every other top performer on the brand.
Roode's main roster debut wasn't ideal in the eyes of many fans as the natural heel debuted as a babyface. And although he soon became WWE United States Champion, he lost it shortly after and wasn't given very much to work within the aftermath. He was eventually paired randomly with fellow struggling superstar Chad Gable, and while they did become WWE RAW Tag Team Champions, they just never meshed well together.
Roode's new character certainly shares similarities to how he was in NXT, but he isn't being given much TV time and has only been featured lately in WWE 24/7 Championship shenanigans. I don't think it's too late for Roode to become a serious contender for a WWE Heavyweight Championship, but if they do not act soon then his time will pass. However, that doesn't mean he can't shine elsewhere, like All Elite Wrestling for example. Roode seems like the type who would be featured prominently in the new organization.