#4 NXT needs more main-event level heels
Outside of the Undisputed Era, who would be considered next in line as top heels? Damian Priest? Killian Dain? The Forgotten Sons? The answer to that question at this point in time is no one.
Had Ciampa returned to NXT as a heel then he would have made perfect sense. But since he overcame such a career-threatening injury to his neck, there was no way that he wouldn't be received as anything more than a hero when he returned. And even though Priest and Dain are being slowly built up as top heels, neither man is ready to be a main-event level threat at the moment.
The Forgotten Sons are also heels, but they are better served as mid-card heels due to a lack of charisma. Cameron Grimes has received the biggest push out of all of the Breakout Tournament participants but he just recently debuted. The biggest and best decision was to turn one of the huge faces to a heel, and Balor desperately needed a huge change. Moving to NXT was the first step. Turning heel was the second part. It will help NXT balance out its ranks while also allowing Balor to explore the nasty side of his personality.