I really, really love NXT. They are doing exactly the opposite from the "main roster": which is doing things GOOD.
The only problem is when someone is "ready" to go to the main roster (specially if they are champions) they have to lose to go there.
The two most damaged about this were Kevin Owens and Sasha Banks, both of them were on fire on NXT (specially Owens who was unstoppable until he lost his title) but after lose against Bàlor he lost his momentum. Same as Sasha Banks, she had to lose the title to "get promoted".
They should do what they did with Paige "you have now a WWE title so you can't still be here on NXT, please give us your title". That was the perfect scenario for her, she didn't lose momentum (at least at that time).
What happens if they want to call Bálor, The Vaudevillians or Bayley to the main roster? They are forced to lose against someone and people who are not so into NXT will say "Oh look, the guy/guys/girl from NXT who lost the title the other night, meh".