The RAF already run 3 fleets. Be under no illusion, the
Js and Ks are totally different aircraft, that happen to share a name and an overall appearance, but different none-the-less.
As the A400 was ordered to replace the K's, there will still be 3 fleets, except the "new" 3rd fleet will be more serviceable and more capable than the "old" 3rd fleet.
The argument over sims is also a moot point. The RAF could never buy a C17 sim, even the USAF don't own any, they merely lease them from Boeing, who run them under contract.
Buying more C17s would only increase our dependence on the USAF training system, which is quite stretched as it is. I mean, they do have rather a lot of C17 crews to keep current themselves.
At least with A400, we become masters of our own training destiny (provided the MoD go ahead with the planned purchase of a sim, of course.)
The basic fact remains that we do not have enough J's to simply scrap the Ks and transfer tasking to the J fleet. Nor would buying more J's help because they lack the outsize load capability needed to deliver some of the army's newest equipment to the front line.
The C17, great as it is, is really not suited to unprepared strip ops. It can do it, don't get me wrong, but those donks really to take a hammering with all the dust ingestion. Add to that the servicing requirements that will be incurred by hammering them in the Tac role, and over the longer term, A400 still wins. (Obviously this is opinion, and I have no figures to back it up)