There are plenty of more types of demons, but I'm not going to bother describing each one. The Amorphous Demons were simply the ones that were there; there are plenty others I could have thrown at you, and it would have ended much the same way. Or worse. Besides, if any other demon did attack through the windows, they would have gotten through the barricades. For all their resistances, Amorphous Demons are reliant on the fact most of their prey are soft fleshy things. I'd say don't look a gift horse in the mouth.