The main aim of any tanker is to get as much fuel as possible airborne and then give it away quickly. Clearly, the Airbus won this competition due to it's 110T fuel load. The ability to carry a lot of freight and troops as well is a massive bonus. The Airbus is in a different league to the Boeing being more modern and more capable.
My company has 18 A330s. They are massive money earners. The ability to carry 35T of freight in the belly means some of our routes don't need to carry passengers to be profitable. In fact, one of our routes is run because of freight instead of pax.