Ok, power train only fast skill progress players. These are players which get more than 4% skill progress per 1% condition lost.
When your player reaches quallity near scout (1 skill point to scout) then stop adding skill point because scouts have drastically slower growth than 5* players. When you gather enough skill points, add them and stop powertraining for that player. More often your player gets training and more packs you spend, more skll points will he get in shorter time.