Flight,
I think your view on how the tankers are used is a good one, but is it the one used during selection?
Bear in mind that the EADS tanker is configured for centreline boom and drogue and can have (not certain if they are part of the order) drogue pods on each wing, so double tanking (USN/USA helos and allies) could happen, as well as large offload...this double tanking potential is an advantage over the 767 as proposed, making th enumbers arguement more complex.
There is a balance to strike (ho ho) between the 'combat' operations side and actually getting the combat capability to the combat area in the most effective and efficient manner as well as the peace time operational tempo.
If we were to consider the 'warfighting' aspect as primary then the 767 is still potentially the wrong aircraft, its too big WRT to its off load capability and airfield performance compared to the A310MRTT; admittedly not offered as in EADS's view the larger airframe offered the better compromise. The A310 would offer, for the overall budget greater numbers of airframes and hence number of refueling points airborne, potentially..and an offload capability that pretty much matches the 767 on a one to one basis, whilst being a smaller plane to locate more diversely etc etc.
The answer sadly is that in order to replace the 135 there were two board approaches.. a similar sized unit which replaced the 135 on a one for one basis (not in the order..) or a larger unit that doubled up with increased capacity and so the overall number could be reduced.
EADS felt that bigger offered the tanking capacity required as well as something more, whereas Boeing stuck to the tanking requirement....and made a clear call not to offer much more.
As for the parts mix, yes they are flying in different airframes and Boeing have made hybrids before very successfully, and as with the boom, offered their massive experience as proof the 'could' do it. But the reality as that Boeing offered a great track record and a design, EADS offered a good track record and a design that was already flying. A fine balance indeed.
But the political battle is only just beginning and the actual capabilites and needs of the warfighters will be overshadowed by the political needs of those assigning tax payers dollars to them.