Frozen pizza usally needs more flavour in one way or another, depending on the toppings ... a good way IMO is usally adding some stronger cheese, not Mozarella. Old Gouda or the likes do the Job well ...
You are right of course. I was thinking of the flavourless "not-actually -called mozzarella"-mozzarella you can buy eveywhere here. The real stuff actually has a very good taste.