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Unfortunately for you, those days are long gone and I would suggest that the opportunity to achieve Pilot from WSOp is technically feasible, but unlikely. Not only because the available Pilot slots are significantly less than they were in my day, but your deskie would also have to fill your WSOp slot while you became a training risk for a new role. Frankly, if you didn't feel you had the potential to sit in a Typhoon from the start of your career, the idea that you would suddenly become a strong candidate after 3 years as a WSOp on Chinook is stretching reality a bit. In all my career, I recommended less than 5 WSOp colleagues for commissioning potential as aircrew - all of them were head and shoulders above their peers in terms of innate ability and potential to succeed in training.
I would therefore reinforce what Schleigg says, and suggest that you aim for the top job (Pilot) from the outset. If you trip up at OASC but still wish to fly at all costs, then you'll have to accept a step down the ladder and go for WSOp. It is a great job and you will have all the satisfaction, fun and benefits of being RAF aircrew, but without the opportunity to achieve the highest level within the service.
Trust me, based on the VSOs I met in the latter years of my career, you'd be better off at a level well below the stratospheric ranks. A level where you could remain true to your own ideals and hold your head high.
As has been said, if you want pilot, apply for pilot. WSOp shouldn't be a deliberate stepping stone. If it later happens to be the only way into the service, and you discount civvy options outside the service, so be it.