Pies take various forms. There’s no rule against covering the crust. Sandwiches and flatbreads have bread as an ingredient. You don’t bake sandwich slices in the oven around a ham and cheese. A flatbread is made by piling toppings on an already baked bread. A tomato sauce, mozzarella and pepperoni flatbread is distinctly different than a pepperoni pizza, no? I could go on and on. There are many reasons pizza is a pie and bread-derived foods are not. Now, is a calzone a sandwich? Still no. More like a hand pie.