There are degrees of nationalism, to be sure. An approach that refuses to allow others into your country based on the proposition that by the happenstance of place of birth there is some sort of entitlement to a certain life, or inherited trait that others cannot possibly have, would seem to be pretty extreme.
The concept that other races or nationalities are inherently inferior is an offshoot of that. I would think most people would accept such a premise as fascist.
Now, that does not mean that you cannot believe in exceptionalism based on things like national culture or the like. But, I think that when the concept becomes associated with believing that its natural, somehow inherited, that you've gone too far.
That is my own thinking on the subject.
Your definitions rely on those stances applying to your accepted ideology and not some actual "extremism".
By the same argument, a belief that literally everyone should be allowed in, just because they happen to want to be there, is extreme. Especially if you believe the government is owned by the people it represents. They want to lock their doors, control who comes in the front door, and make sure no one breaks in the back door. That's hardly extreme, unless you hold the opposite view. Apparently enough Italians hold the belief, hence her election, so it's not extreme at the national level.
Historically it makes good sense as Italy has seen tons of devastation from outsiders pushing their way in. Like everything migration needs to be controlled, or else it becomes too much and damages the country.
Your fascist argument is laughable. You even use the correct term in your attempt at definition. Nationalism. You can be nationalistic without be fascist. Fascism is just the scarier word. Racist may even be a better fit.
And how is believing you inherent a national culture going too far? I cant just claim Brazilian culture. Just because I spent 2 months there doesnt mean I have a claim to it. Just because they tell me I dont have it, doesnt mean they are extreme.
Your use of vague language is intentional to make your disagreement with another's opinion seem morally, and maybe intellectually, superior in some manner.
It's the same degree of bigotry you are claiming to decry, just applied along different lines.