What he means, of course, is that soup by itself is not substantial enough to satisfy hunger. In some cases he may be right, but in the case of soupe au pistou he is completely wrong. This soup is very filling, healthy and absolutely delicious. My flatmate and I survived on it while we were in college.
You can vary the vegetables according to what you have available or what's in season (courgette, squash, peas all work well). Any vegetables that cook quickly need to be added a few minutes before you serve otherwise they will dissolve.
For the soup
Four Seasons Food hosted by Delicieux and Eat Your Veg