JCA is a maritime strike requirement, for which the money for a GR4 replacement was sacrificed. My point being that this unpalatable fact somehow got lost in the chaff of SDSR and reference to a GR4 replacement has been made ever since.
I honestly believe that there is still a general supposition that GR4 is to be replaced - even if not by DPOC which (I stand to be corrected - my sources are those openly available from parliament) is now no more.
It is also my belief that the dawning realisation of where this will leave the RAF (which you are totally correct about) is a mainstay in the 'revert to STOVL' thinking. i.e. we get DPOC back. Do you think we really will though?
So your point is entirely accurate - if JCA falls over there is a chance that it's Typhoon alone. Horrendous.
I think we do disagree on one thing. We are a small island nation - so the fact that others make do with dedicated land based air might have no direct read across to us. An extension of this argument might be that we should not worry about our current lack of MPA (in my opinion the single biggest error of our time) as Switzerland seems to have managed without one for years.