P_S,
I must admit that I was basing my argument on a UK IT carrier, whose sponsorship programme I know a little more about. It is certainly the case with them that there is no significant additional costs attached to training their own aircrew. Combine this with the fact that they can control the process to get aircrew of the standard they want, when they want - it has to be an attractive option to an airline! At the end of the day, the airlines wouldn't run the programmes unless they saw some benefit from them.
I do fully agree with you that self-sponsorship shown total commitment and determination, and at the end of the day, airlines must get most of their crews from this route.
Regards,
Cuban_8