In short - location, location, location....................
Saint John has the port, and, Irving heavy industry
Fredericton has the government, the university and the military.
Moncton has transportation, distribution, central location and bilingualism
These factors define each city, and, provide a stable base for each city to grow and prosper. This is not going to change. Cities should play to their strengths. All three cities are destined to prosper.
I just tend to believe that the underpinnings of Moncton's economy will create greater growth than in SJ or Freddy. Momentum is also important, and, right now, Moncton has that in spades.
Could this change? Sure!!! Maybe small modular reactors will be destined to be the energy saviours of the world in which case SJ will make out like a bandit. This would be fantastic for the entire provonce. We just don't know what the world will be like in 20 years time.