That really seems like a wash, your later training in whatever is slowed down by just as much, plus you get your skills out of whack, which gives you a penalty to training.
Basically, there are two paths, going with balanced training (my strategy) will result in a slightly better player, but will waste some resources getting there. Doing all of the single position training first will allow you to focus resources more effectively, with a loss of a little bit of training efficiency, due to out of balance skills. There is of course also a compromise position, where you do mostly one position, but during the allstar week and other weeks with only two games (offseason) you do two position training.
I don't think you are taking into consideration the fact the original poster is in a higher league than you - he can train more unevenly as his income probably won't affect his ability to sustain his trainees wages (unlike those in IV or V series).
You also fail to justify how one week he can suddenly switch from 3 trainees to 6 (when you want to train a 2position only skill)... where do these other 3 trainees magically come from? There is no hardship to train Stamina or FT during the times he has only 2 games. If the players are getting 1 position training enough then a break here and there wont be so bad.
Your strategy might end up with a better player for you and the division you are in - for him in Division 2 he needs or will need the OD/PA to eventually promote and then hold his own in the top division in his country that has only 40 odd users.
A rounded Proficient guy will be nothing more than a decent bench player - he needs higher skills in key areas.