Anyway, I don't think our discussion is going to arrive anywhere.
You ask for Krugman (who is a guy that I like by the way) opinions:
https://www.cnbc.com/id/46944145
For me, what he says there is in clear contradiction with (for instance):
https://www.sciencedirect.com/science/article/pii/S105752191...
It seems to me that whatever it is what they put in their textbooks, even more important is what they put in their models.
Here there is a good criticism of Krugman views: https://www.nakedcapitalism.com/2012/04/scott-fullwiler-krug...
But if they didn't solve it, we are not going to neither.