#2 Robert Roode
As of this writing, Robert Roode is currently one half of the WWE Tag Team Champions on RAW with Dolph Ziggler, so things could be worse. However, they were never better for the Glorious One then when he was in NXT.
Since his arrival on the main roster in 2017, Roode has been the WWE United States Champion and had also previously held the Tag Team Championship in a tag team pairing with Chad Gable.
Even so, he has spent far more time miles away from the spotlight, than in it. Although Roode is a good mid-card heel on RAW, he was the biggest and best in NXT during his lengthy reign as NXT Champion.
This is just something that WWE is really missing out on. Roode was an incredible heel but seeing him on RAW is like watching a completely different Superstar. Roode made NXT his own and if he returned, I don't see why he couldn't become the main event player he was before.