I tried to draw my ideas on the picture.
"Soldiers now have diminishing returns on attribute gains (so their base stat rolls are now more important), which also allows rookie soldiers to progress fairly quickly without breaking the game balance." (taked from "What are the differences between Xenonauts 1 and Xenonauts 2?")
So a strategy in which a soldier class is selected at the beginning of a recruit's career may be useful. It is difficult to do this in the Manage Soldiers window, because sorting by characteristics will lift veterans up. So it would be convenient to assign roles in the Recruit Soldier window, where all soldiers have the zero level.