I agree with your fact in part. Yes, 64% of personnel leave around their 3-9 year point, but it is the costly 20% that leave around their 16-24 year immediate pension point that I suggest is being targetted. The very few that go the full way to 55 (soon to be 60) number less than 2%.
There are HUGE savings to be had if you reduce the number that make an immediate pension point or early departure point.
But (in the aircraft techie world) the savings is offset by the loss of suitably qualified and experienced personnel.
A kid straight out of school won't have the experience, skill set, knowledge and more importantly these days... the auths to get an ac serviceable when you need it. Bear in mind when kids leave Cosford they're still not auth'd / qualified, especially to work on Typhoon.
It's the difference between spending all night looking at a fault, chasing your tail and the ac still U/S after the shift has ended and an experienced guy having seen the fault before and knows how best to fix it.