Brain - nobody has said guys need to be gym monkeys, size zero or marathon runners - there is nothing wrong with carrying a bit of extra weight either (I've been doing it for years) but GW was criticising guys with physiques so at odds with what one might reasonably expect from someone in the Armed Forces that they become ridiculous.
It is possible to be 18 stone and very fit (see international rugby players for example) but they don't have several michelin tyres of fat stored round their midriffs and they do a shedload of phys every day to stay in shape.
You don't look at some 20 stone lardie with a lager in his hand and think 'I bet he's good at his job' do you? You think 'Fat git, needs to spend less time in the pub' If you think it is the right image for the RAF to project then you belong in a very different RAF than the one I joined 26 years ago.