No establishment is a holy cow: the die in a ditch issue here is service identity/esprit de corps. I suspect that the defence Training review is looking at the Lympstone model which seems to work well for the Booties. Plenty of spare capacity alongside depleted recruit classes in single service training establishments, with the Army, as ever, insisting on keeping orficers and chaps apart - pobably the price of accepting further Regimental mergers/losing so many tanks.
Much of these "historical" issues are really quite recent - late Victorian say. BRNC 1905. I wonder what the outcry was like when Confidential Reporting came in, not to mention the abolition of purchasing commissions.
BRNC and Cranwell are not important: the battle of Britain and the Battle of the Atlantic are. Every Establishment that closes is painful, but the service survives. The traditions of fighting and winning agaisnt odds are what we are about. Often enemies have included the prliament and the Treasury: ther's a fine continuing tradition!