Well if Puma gets axed and Merlin goes to the Navy, the RAF will have a totally unbalanced capability which won't be FCOC compliant. Given that the doctrine wallahs are predicting a future of complex interventions in littoral / urban environments, that is going to need at least some relatively small, flexible RW assets if the RAF wants to operate SH in that context.
As we found all too often in the early days of HERRICK, trying to get CH-47 into small compounds doesn't always work, and you either end up a) trashing the cab b) trashing the compound or c) doing an insert to an offset HLS and having to fight your way in and out - which is just about fine in a relatively open area, but do you really want to do that in an urban environment?
Unfortunately, much of this seems to have been overlooked and hasn't been helped by the Chinook mafia dominating the RAF's RW decision making and planning processes. So now, given that we are skint and that Puma isn't on ops, regardless of the capability requirement for a reasonably small and flexible platform capable of operating in all environments, anything we might say will just be seen as a fighting a rear-guard action by the Army and RN who will quite happily see Puma go.