These debates mirror the bean counters view of warfare and military hardware.
The 5th C-17 is a very low risk acquisition given we have the rest of the support infrastructure in place. Makes good economic sense.
Bit like the Super Hornet buy given that we are buying an upgraded model of something we are familiar with. This I'm told was a big reason rather than going for the Strike Eagle. The crews require around a five hour conversion from the A model to the F model. Of course F-111 drivers and WSO's are different but they would be with whatever was purchased.
The J model Herc was another good buy for the same reasons.
Helo wise, the M model Blackhawk and some more Chinooks might have been a better option than the MRH90. Works for the biggest user of battlefield air - the US Army. I was told at Avalon by someone at high Navy operational level that the MRH90 has some big limitations for at-sea operations - no auto blade fold [limits ops in heavy weather etc] and the composite structure cannot be field repaired like metal. The corrosion argument is a furphy as the 37 year old Sea Kings don't have corrosion issues but rather old and unreliable avionics.
The message really is to cut your cloth to suit your budget and ops needs, not either of these.