So the fight with Kaga will be impassable?
Kagha simply shouldn't be labeled an archdruid. "Acting archdruid" or "regent" at best.
Halsin as the "proper" archdruid of the area on the other hand surely shouldn't be a level 5.
Power tuning aside, in any case, the point is that the level shouldn't be a label clearly readable on characters (especially not monsters, that aren't supposed to have levels to begin with) but if we really HAVE to (because as the time goes it seems that Larian hates everything that's good design, somehow) at least that level should make sense in context and be consistent.