ponders

I don’t know how one would quantify “heartiest”.

I guess if one uses caloric content, it’s probably something with a lot of oil, since oil is about as calorie-dense as you can get food.

Plus, you need it to “flow”, water doesn’t have calories, and so you’re going to want a liquid to replace water as much as possible.

Oil itself is drinkable, though I’d guess that you probably wouldn’t count it as a soup.

How much oil you can add to a soup – because various recipes I see online do have recipes suggesting “add to taste” – before it stops qualifying as a soup is probably not well-defined anywhere.