#8 Eric Young
Former TNA Impact Wrestling World Heavyweight Champion Eric Young had a pretty positive debut in NXT back in 2016 as the leader of the faction SAniTy. The group feuded with NXT's top Superstars and became the NXT Tag Team Champions. They would be drafted to SmackDown on the post-WrestleMania Superstar Shakeup in 2018, but it would be three months before the actually debuted on camera.
Following their debut, they were sparingly used on SmackDown and were mostly on the losing end. They were split up during the 2019 Superstar Shakeup and ever since, EY has found himself chasing the new WWE 24/7 Championship, to no success.
Now while I am actually finding the 24/7 Championship matches/segments entertaining, they still could be doing much more with Eric Young. Unfortunately, it seems like they have zero plans for the Impact Wrestling original, and it's probably time he returns to life outside WWE, for better opportunities.