The above conditions are being flagrantly disregarded. As I stated in another post - many many SO 's have plenty of experience in jets and qualified for JFO upgrade from the day they joined. Only reason they are SO 's is thats what was available at the time. Also not all can join on a base due their nationality.
DEFO is one thing only - saving two upgrades in times of low training resources ( ie SO to FO and new SO to replace him/her ) and secondly saving money cause guys get hired on bases.
Slightly pointless post - I know - since nothing said here will change that