I could see how the team making garrisons and the team making raids could be the same team. I mean, they have to make buildings, NPCs, interactable objects, etc. So I could potentially be convinced that garrisons was why we had only two raid tiers. Maybe.
I can't see how the team making spells and/or the team making artifacts was the team making raids at all. And you would not be able to convince me they are.