There are many different groups centralized around patriotism in many different ways that you could single out.
And these patriotic groups would be representative of the whole? Or just poorly educated outliers? Who are these individuals? And who do they represent exactly?
You don't think human psychology is consistent across cultures?
No. Not really. Thinking, logic, and reasoning differ enough from culture to culture to necessitate an entirely unique discipline called ethnology or anthropology. Also clothing, food, taste, values, love, hate, concepts of good and evil, basically everything that makes us a social animal. Including narcissism.
It's overreach. The scientific method has it's limits. And we're obligated to know them and not pretend that it can be applied to everything and yield similar, dependable results. That's posturing.
And literature gives a better account of nationalistic narcissism than social science could ever hope for anyway..
"Nationalism, on the other hand, is inseparable from the desire for power. The abiding purpose of every nationalist is to secure more power and more prestige, not for himself but for the nation or other unit in which he has chosen to sink his own individuality"