You're half right. You could pop off and do CTC's deals for a bonded £60 000 or something.
Thing is, you're looking at trading a bond of £60k ish for a 12+ year career, where you can't get any relevant qualifications, you might die, and you might end up flying helicopters which means you don't have a hope in hell of getting an ATPL(A) anyway.
You are probably looking at several tours to get anywhere near the number of hours to qualify for any exemptions to ATPL theory, but you still have to pay to get a multi engine IR, an MCC, and several other things. If you leave at that age, then you're close to unemployable by an airline anyway, and if you leave earlier, add a large bill for your ATPL exams too.
Without being too offensive, with today's climate when it comes to government spending, why do so many people seem to think that the RAF exists to train people to be airline pilots in a couple of years' time?
It doesn't do that, it doesn't work like that, and if you don't want to potentially spend the next decade having your Chinook shot at in Afghanistan, don't join. You simply won't make it through any of the training, regardless of anything else.
And yes, I'm a pilot in the RAF.