[...] besides, theres actually quite a few units (weapon teams/snipers, etc) that dont follow the pattern of normal vet bonuses, so unique vet bonuses arent new.
I'll just address this - while what you say is true, up to this point all units in their respective "groups" ("combat" infantry like grens or conscripts, indirect fire units like mortars and artillery etc.) and sides had the same veterancy bonuses.
So right now, Assault Grenadiers are the only "combat" infantry which vet isn't following the same path as the rest of units from it's group.