Then how does one justify experienced soldiers as getting 5 more levels of veterancy?
Grenadiers are also described as experienced troops (quite the opposite of concripts) but they still get 3 vet ranks just like cons.
It's just basic faction design. It doesn't matter whether a unit already represents experienced troops or not.
EDIT: I don't have problem with the term "obersoldat". I think the name represents their combat effectiveness quite nicely.