I, for one, don't agree with having to pay for an endorsement, but sadly that is the way things are today. How then, essentially, is that different from Jetstar or Virgin for an entry level F/O - or have I missed something along the line? If they were to take a Jetstar gig, wouldn't they have to pay for an Airbus endorsement and if it was with DJ and they didn't already have a 737, wouldn't salary sacrifice some into it?????????? To my knowledge OA doesn't bond you and you can leave on a month's notice if you wish.
From my contacts in the know, the retention rate is actually pretty good. The last departure was an F/O who went to QF about 12 months plus ago, and that certainly was for the money alone such was his priority. The current F/O's, however, aren't so mercenary and I think you'll find, T-B, that several have been there for bordering on a couple of years - not too bad for allegedly such a "poor" job.
I think RB has it in one, time the doomsdayers actually spoke to people rather than guesstimate what they are thinking.