That sounds like a statement that should follow, but it doesn't.
Disclaimer: I'm not saying working in an upper level defence post makes you fit for running anything, and it beats me how some people get up the ladder. However ...
Ex-RAAF can and do run businesses, and (for the right individuals) their higher level defence work makes them pretty good candidates for other top jobs.
The budgets they have had to manage are far from limitless, the people they lead do not simply jump to obey, they need to know how to work in and provide direction for large and complex organisations.
Generalising about this stuff isn't appropriate. I've raised the question before about what is the right breeding ground for people to fill these kinds of senior post, without suggesting that ex-military is the only way to go. It's one obvious route, but what are the others? Small business owners would probably be out of their depth, and yes, some ex-military aren't suitable either, but don't tar everyone with the same brush.