Hi
At the beginning, I did not agree with you at all, but, now, I think that country like NZ probably need a combination of both, in the NT need to play the best players that NZ have,but I also can agree that players that have short way until they reach the level of the NT (less than 2 seasons of training for example), need to be in the NT, the others - need to be in contact with the coach of the NT and continue with their training.
*This was definitely not my original idea, but probably in the case of a country like New Zealand, that at the moment, anyway achieving 2-3 wins on the season, would be really more smart to develop the next generation, but, I do not think it would be right to neglect the current generation, so, after your questions and suggestions, I think it would be right to combine, something like 10 best players in New Zealand, plus 6 best young players in New Zealand, plus two empty places, for special cases (game shape problems, or injury to a key player, or something similar)