Last time I was close to this, it had been agreed that RN harmony figures would be applied to all in the Lightning Force if required for delivery of the Carrier Strike capability. No idea whether that policy remains in place.
The comment about some RAF fleets doing 'only' 3 or 4 month deployments is neither here nor there. The repetition rate of those deployments can be very high. Each Tornado Force squadron has done 6 months on ops in the last 12, and the Typhoon Force practically the same when MOD-directed overseas exercises are factored in.
Both services will suffer in the long run for the outsourcing of so many 'shore postings' such as training establishments; harmony figures used to be considered a medium-term management aid rather than a career-average measure, and running them close year after year is not a recipe for retention. But then, I can't help whether there is now an unspoken strategy of leading people towards shorter, more intense regular careers. There would be many benefits to doing so; trouble is, such a strategy needs recruiting (Capita... ) and training (MFTS...) systems that work well, and a risk appetite that can accommodate larger numbers of less-experienced workers at first line. Hmm!