I was speaking to 3 different training/checking captains from 2 different airlines recently, all of whom ... by far the ones with the most difficulty have been those from GA
Even if the experience held by a GA pilot somehow makes a cadet easier to deal with for the trainers, the captains I know that have to fly with them after the line check certainly have a very different opinion. Situational awareness, airmanship, etc. - fairly important stuff, and not something that can be taught over the period of a cadet's training.
I wonder if the REX check pilots would be happy to train the the cadets on kingairs out of essendon and cut them loose on their own? If 200 hours or so isn't good enough to send them out on their own in a twin turboprop, then they sure as hell shouldn't be in any airliner except as perhaps an SO on a longhaul jet.