@ska normally I would agree if it was added raw - in this case I blanched it in salted water and then slowly sauteed it with the carrots before adding it to the soup, significantly less overpowering that way.
on top of that american grocery store celery is bland as hell anyway. if it was fresh celery from a local farm I'd use half as much, but our farm share doesn't start for another 8 weeks or so :(