Hiring substantially more FOs than you have CAs to fly with just slows the experienced FOs from getting the hours they need to upgrade. Slow them enough and the experienced guys say screw it, I can fly my butt off as a junior FO at one of the ULCCs and they leave planning on getting a new type and enough hours there to be competitive for their career airline. Unless you are DEC eligible, new hires are going to have to wait a mite. If you ARE DEC eligible you go to the head of the class.