TBH the main roster guys shouldn't be there, I don't really see what the point of them appearing on NXT TV is. If we're talking about people like Percy Watson and Bateman who never appear on the main programs then yeah, but for guys like 3MB and Epico & Primo it's just a waste of time.
I think they do have a purpose, which is maybe being a draw of sorts on a lesser level.
But I feel that they should be kept separate from the NXT guys. Like if WWE guys appear on NXT, they should either be wrestling other WWE guys, or getting wins over enhancement guys like Aiden English or Jake Carter. They shouldn't be treated as possible contenders to the NXT titles or regularly interacting with the developmental talent.
It creates a weird situation. The main roster guys can't win the belts, but losing to the NXT guys makes them look weak, because they're basically jobbing to minor league guys. Also it looks stupid because kayfabe wise, if an NXT guy can actually beat a WWE Superstar, why is he still on NXT?
If a main roster talent like Alex Riley is booked on NXT, he should be treated like a "guest star" rather than "one of the boys". It should be like The Rock coming back to RAW, but on a much smaller scale.