I make it 16% not 25% but that is just fiddling.
As for over recruiting and getting top heavy, over recruiting was a policy at one time in anticipation of increased exits at the other end.
Yes someone does keep an eye on the figures for lets say 6 years or so in advance
Seriously, from the RAF website it would appear that WSO are only being recruited on short service commissions. For anyone who wants a career in civvie street in their 30s it looks a good deal. For anyone who wants acareer in the RAF - dead duck.