The intelligent source is Matthew Yglesias who reports on a conference call with Gates
On specifics, Gates said that the problem with the Army’s Future Combat Systems program isn’t just the cost. It’s that there wasn’t enough flexibility. Based on the operational lessons learned in Iraq and Afghanistan, it’s useful to have a broad range of different kinds of vehicles, and it wasn’t proving feasible through the FCS process to design a system that could replace the full spectrum of currently available vehicles.
The making an argument in a news article (and making it badly) sourse is Jeffrey Smith in the Washington Post who writes
the V-shaped hull of the costly Mine Resistant Ambush Protected vehicle deflected the worst blast effects of buried explosives.
Within weeks, and after some pointed demands for the MRAPs from Capitol Hill, Gates decided to make accelerated production of the vehicles his top priority, using a special task force that circumvented the department's normal purchasing methods -- and the initial opposition of the Army and the Marine Corps.
Putting the relevant but abstract argument by Yglesias and the praise of Gates tangetially (if at all) related to the current debate by Smith together, I guess that Gates argued that if "Future Combat Systems" were "Current Combat Systems" it would have been even harder to get US service people in Iraq safely in V shaped hulls.
Even without having to give up fancy electronics to save lives, he claims the Army and Marine Corps resisted his efforts. His argument seems to be that, if service people had been trained so they were dependent of FCS electronics and no FCS MRAPs were available (a lack of flexibility that) more Americans would be dead by now.
That seems to me to be an argument devastating enough to shut Senator Inhofe up, if anything can (but obviously nothing can).