#4 – Apollo Crews
Apollo Crews' stay in NXT was short. From making his NXT debut in August 2015 to making his Main Roster debut in April 2016, Uhaa (his real name) had a very short stint in the developmental brand.
He had just one shot at the NXT title against then champion, Finn Balor. Crews did win the match via disqualification, but that was about it. He was involved in a feud with Baron Corbin, who had caused the disqualification in the title match, and then there was another small feud with Elias before he made his main roster debut.
While the other three mentioned in the previous paragraph are in a decent position right now, Crews is lost in the script. He does not have a feud going on with anyone nor does it look like WWE are planning to give him a push.
Sending him back to NXT can help in keeping him happy and also rebuild his confidence while he has clearly lost since Titus Worldwide was broken up.