From D.IV and up, 2-position training gets you nowhere as you fall back too much compared to the teams that do 1-position training.
I got to DIII using 2-pos training exclusively.
It's easy to train 5 guys with 2-pos training maintaining good GS and winning.
It's harder to win aiming to 1-pos train 3 guys.
Unless you can afford a level 5+ trainer, you might as well improve half of your team as opposed to quarter.