Half right tho? It was a point of his character that he dislikes being too much stronger than his enemies, because itmakes it too "easy", so while he is one of the Primordials (And a noble Duke/King, which is only a title tho, like with human nobility) his Evolution at the point of summoning is Arch Demon, not because he couldn't evolve, but because of his "weird" nature he never wanted to, so he has strength at that point that far suceeds other Arch Demons because of his experience, but he still s a arch demon nonetheless . After he is named tho he does evolve into a Demon Peer .
Seems that can be translated as Demon Lord, but he isnt a Demon Lord like Rimuru in the sense, it is "only" the race evolution of the Demon race over the Arch Demon (well, comparable to real Demon Lords in strength, but still, different thing)
Point is, AT LAST HE IS HERE