If you could see the galaxy as brightly as in the photos, there's nothing to indicate its size, at least not directly. You are saying it can't be close because

If you could see the galaxy as brightly as in the photos, there's nothing to indicate its size, at least not directly. You are saying it can't be close because it has a trillion stars, and we know stars are big, therefore it is big, therefore it must be far away, and then back to therefore it is big. Isn't that kind of circular? I could imagine ancient people seeing a galaxy that size (if it was bright enough), and guessing it was a few hundred miles away and under a hundred miles across.