I would argue that the point of Next Stars, is to take Next Seasons NBA Stars", polish their profile a BIT, and give them better development which then benefits them in their first NBA season.
Guys like LaMelo, Giddey, Hampton, were always going to play NBA, and probably always going to be drafted relatively early. The NBL didn't create them, it just helped them along a little. PLUS I would definitely say helped their transition to their first NBA season.
So whilst I don't know why Armstrong and Nikita didn't thrive, we have to assume that for whatever reason they just weren't that good.
So ok, maybe they would have gotten more minutes in a College team, (assuming that was even an option?) but that still wouldn't have got them to the NBA.
I'm often surprised at the apparent ease with which players can play internationally, but I think its a given that if somebody wants to play in the NBA, then they need to be able to communicate in English.