Can't speak for WestWind at DVT (havn't trained there since 94). At Chandler Air Service we only hire those that we have trained, but it is not a guarantee. Supply and demand. Our current cadre of instructors are an older group. Our youngest is 35 and the oldest is in their 60's. Also we are have a tailwheel and aerobatic specialty, so we look for instructors that want to stay more long term.
As far as teaching in multi, an instructor that is an assistant chieft and has been here for six years, is finally getting the nod to get his MEI and teach for us in our Aztec. First though he taught primary for a few years, then tailwheel and aerobatics for a few more, assigned to assistant chief status and now will be doing his MEI. Though honestly, he could care less about going to the airlines.
We have had many go to the airlines and move on over the years, but our structure has changed and alot of our instructors are now career instructors. I myself have been here for almost four years.
There are few traditional FBO's left in the Phoenix area, with a majority of the instructor positions being at the foreign academies.
And actually, to the Transpac instructors, either you guys have done alot better with the language skills of your students, or we are just getting used to them, but sounds like things are getting alot better over there.
Good luck.