in the past people ate half a can of soup for lunch. Not in our house they didn't. Back in the 60s and 70s my Mum would probably have made one tin of condensed soup stretch to four small servings but that would have been to serve as a first course at a main meal, with a substantial main course and pudding to follow, and there would have been bread on the table to have with the soup. If we'd had soup for lunch it would have been her home-made broth or lentil soup, both of which were so thick you could stand the spoon up in it, and there would also have been bread available, and probably the fixings to turn the bread or roll into a sandwich (cheese, cold meat).
I love soup. The only soups I would even consider eating without bread are the ones that are full of very filling starchy things like rice, barley, pasta, potatoes and beans. However, a large part of the joy of eating soup for me is dunking good bread in the bowl, so soup is not a slimming option for me. I made minestrone with the stock from the turkey carcas and it was excellent. Beans, celery, carrot, onion, courgette, cabbage, tin of tomatoes, tomato puree, turkey stock, orzo, salt, pepper, basil, oregano, bayleaf, sage, thyme, pesto, olive oil, garlic. Several tubs in the freezer. They are not small portions.