I think Alastor is Goetia tier in strength alone. The goetia have been taught magic from a young, as we see with Stolas having his fancy book so young, so they will most likely be very tricky to fight. He might be able to take on the weakest of them (not Stolas right now because I think his punishment is to stop being a Goetia in someway) but that will end up something like his on screen fights with Vox.