It began to increase fast. Tens of millions died of famine under British rule. And so on. You have to decide what you mean by the term before answering. In my view it was a remarkable advance.
Huge problems remain, but that's a separate matter.
Afraid I don't follow the reasoning at all. The cases you mention require close analysis and have all sorts of aspects. I am a bit confused whether nationalism in any sense can be progressive, including and in fact referring specifically to nationalisms of people in the third world. I have had serious discussions on the issue with a Marxist Professor of mine. This professor believes that nationalism is based on the unification of all classes of a society, and that to him is most undesirable.