Yes, some schools -- notably the Sarvastivada -- taught that dharmas "exist across the three time periods (past, present, future)". That doesn't necessarily mean "permanent and unchanging", but at any rate it is a straw man. The Buddha's declaration of the irrelevance of such ontological speculations suffices, and indulging in arguments against them is merely stepping into the ontological cesspool with those who argue them, and turning that romp in the slop into a Whole Nuther Religion. And how is the following (from SN 35.85) not "ontological"? Then Ven. Ananda went to the Blessed One and on arrival, having bowed down to him, sat to one side. As he was sitting there he said to the Blessed One, "It is said that the world (loka) is empty, the world is empty, lord. In what respect is it said that the world is empty?" "Insofar as it is empty of a self or of anything pertaining to a self: Thus it is said, Ananda, that the world is empty."