The thing that's stopping us from having a professional league isn't population, it's the fact that we have a very competitive sporting market. If you think about it a city like Dunedin with a population of 127,000 has two professional rugby teams, a professional cricket team, as well as semi-professional netball, womens rugby, football, etc.
Compare that to other markets where a city like Austin can have a population of more than two million people and yet have no (current) professional teams.
I think the word semi should be out in front of two of the three teams you have highlighted
No way you could say the volts are fullly professional and the same would apply to the NPC Team.
Both would be semi