I have heard from so many sources including the game manual, Gms and NT coaches that NT games does increace experience that we will have to agree to disagree on this point. I have heard that it does depend on how much you play so playing 1 minute here or there probably wont actually give that much of a boost.
the difference in speed is minimal.
In terms of there not being much difference I will also have to disagree. Again just going by the Hungarian NT database and training analysis. I can't compare 19 and 21 but I can compare 18 and 20. I have two guys the same height and 2 years apart, 18 and 20.
1 position training in pressure with a level 6 trainer.
Nick Covic 18 193 cm 2.00
Barton Melmeth 20 193 cm 2.44
That looks like a massive difference to me. For every 4 pops Barton will get Nick will get 5! By the end of the season that could be the difference between our guys having prominent defence and sensational defence. I know which one I would go for.
I totally do agree with you that the biggest factor is the manager ensuring that they get 48+ of single position training every week and are kept in great game shape.