If you are cooking a single ingredient and only trying to exemplify the flavor of that one ingredient, then yes, I would have to agree that you can make a very flavorful dish without too much fat.
The problem presents itself when you are making a dish with many different flavors you want to be blended in the final dish, and only fat makes that happen. Fat has the peculiar property of absorbing the flavor of what is cooked in it and then transferring that flavor to what is next cooked in it, but then also absorbs the flavor of the 2nd object, which is then transferred to the 3rd and so on. No other ingredient can make this happen, which is why a dish that is braised (which is involves searing all ingredients in a fat at the beginning and then slow cooking the entirety of ingredients with the fat still in the pot) produces a much better result then using a crook pot to cook the same recipe without any searing.
When I cook a vegetable soup or stew, I mix in 12-20 different ingredients, chopped into small pieces. They all blend wonderfully without oil and make a very flavourful dish. Years ago, I used fat or oil for caramelizing onions and carrots, but now I saute them in water. Then I add the other ingredients, but no oil. I agree that a bit of oil wouldn't hurt, but that soup is so good that I don't miss the oil at all. Initially, I worried that my guests won't like such a soup, so I offered them usually only half a bowl to taste it, but without exception, they all like it, so now I give them always a full bowl.
For my all-vegetable soup, I use the following ingredients (I may omit some, depending on what I have in the fridge):
onions, garlic, celery, carrots, potatoes, mushrooms, green peppers, zucchini, eggplant, can of diced or whole tomatoes, apple, rhubarb or lemon, peas or corn, kale or swiss chard, and following herbs - dill, rosemary, basil, parsley, and spices - cumin, red paprika, black pepper, salt and cayenne or crushed chili peppers. At the serving time, I add a dollop of sour cream and finely chopped curly parsley. It is indeed a rather unusual soup (or stew) and for first-time samplers also a good conversation topic.
So, no, you don't need any oil to blend all these ingredients into one flavourful mix. The combination of all these ingredients and spices works very well. You have to try it - with and then without oil.
The stew uses similar ingredients, and sometimes also a plantain, okra or some kind of beans and it is served with pasta or rice. All cooked in one large pot, which will last up to one week or I freeze some of it.
You need one knife, one chopping board, one mixing spoon and one large pot. Washing the pots and bowls is also easier. The pots get never greasy from the fat or oil.
