A couple of points
The Voyager carries twice a Victor load not 3 times and burns at a higher rate. That said to my mind the RAF missed the golden opportunity to buy the KC10 when it was offered back in the late 70's (as well as choosing the wrong ac when we got the Tri*). For example 3 KC10 s could have supported 2 Vulcans attacking Stanley Airfield (it would have needed Tanker/Tanker transfers of course).
The reason for AAR consolidation in modern ops is to maximize the oft-limiting factor of tanker availability especially in a reactive situation. So instead of a number of ac with a small offload with little chance to contribute to the mission you end up a replenished ac which can support the task especially when the plot changes. It has nothing to do with how much fuel a particular ac has -we never seem to have enough fuel (or indeed the correct tanker config )when needed.