Is calzone considered Hamotzi if the main part is the cheese?
Yes. Assuming that the dough is a Hamotzi dough and not a Mezonos dough.
Being that that dough is there to impart flavor, and it’s satisfying to the pallet, it does not become nullified to the cheese.
If the reason you are eating the calzone is for the cheese alone, and the bread around the cheese is merely to hold the cheese, and there is no pleasure from the flavor of dough, it would be Shehakol.
ברכת הנהנין פ״ג ח.