NAB,
Whilst you are absolutely correct about the requirement I think we might be under estimating what an EASA equipped aircraft brings to the party. And we could argue all day about weapon fits. The F-18E is IMHO more of a F-35 'minus' than a GR4 'plus'.
Not sure any allied power would like the idea of an embedded mercenary squadron. Far more palatable to disperse the same amount of people through out the fleet, after all with no deck to fly from the UK has no requirement for a formed Naval Air Squadron (for now).
I'm personally in the 'buy F-35C' camp, but can see how valid the 'look at F-18E' argument is.