Fewer tankers is all very well if you don't need the capability at different locations simultaneously. Half the size in 2 locations is often preferable. In fact, virtually always preferable.
We call it 'hoses in the sky'. A multi-tanker cell is often needed to refuel a large strike package. We used 3 VC10s and 8 Tornados in GW1 not because the VC10 had insufficient fuel, but because all receivers needed to be full close to the release point. They couldn't have done that if they'd had to rely upon a single large tanker.
Equally, no point in huge offloads if the one and only tanker goes U/S on the ground...
There is safety in multiplicity, particularly for critical missions. If Boeing haven't learned that yet, then they truly are showing their naiivety in offering a 777-based tanker.
A310MRTT or A330MRTT offer far greater flexibility and efficiency than any Boeing offering.