I would never train JS whatsoever. And I don't recommend it to anyone
I one season of JS training you get something like +4-5 JS, +2 HN & DR and some bonus (whether it's JS for guards or wingmen). If you train one on one for forwards, in one season, you get about +7 DR +4-5 HN +3 JS + 3 IS. I don't see the point of JS training
i am quite sure you get lot more JS pops then in your calculation, and less IS ups with one on one training(and that also depends on position).
Additionally, the bonus of JS is quite intresting, because JR isn't an training with lot of pops.
And you could argue that the majority of pops, have few effect on game ... the italian nt play(ed long time) with guard and PF/C without driving, and they guard had pretty similiar skill then other top nations(through the cap and elastic) but they also performed on a high level. So at least i train one on one mostly for the secondary pops, while i train JS for the primary ones so i wouldn't only compare the amounts of pops to judge a training.