it comes down to experience
I think there is a natural tendency to think one's own background is best.
For the record, I fly for a medium sized (abet highly respected) European airline which does run cadet schemes, however I wasn't one. I joined my airline with minimal hours and have approaching 2000 hours on type. I have just about enough experience to realise just how much I have to learn. Due to expansion, my airline, which traditionally has had a very long time to command, is upgrading pilots to command with minimum hours, at the same time hiring copilots of varying backgrounds in large numbers.
I've been discussing this topic with a number of colleagues. Put quite simply, the general view is upon being released to the line, a copilot with 1500 hours of SPIFR on a Navajo or similar will be far more use to a commander than a cadet pilot with minimal IFR experience. As much as anything else, the Navajo pilot will have experienced in copying down clearances, negotiating with ATC, slots etc. He will also have experience of running a commercial operation with commercial pressures that come with it, such as practical considerations to consider when planning to fly right down to Wx minimums, juggling the figures to make the loadsheet legal, etc. His handing skills will be more developed too, although this is an area were 'bad' habits can creep in.
However, the consensus was that once the Navajo and cadet pilot have 3-4 years of experience within an airline, a commander would be hard pushed to tell the difference. At this stage of a pilot's career, their innate qualities such as their temperament and mental capacity are far more important. It's these qualities that make a pilot good or bad, and can be assessed with some accuracy during a well thought out recruitment process, irrespective of a pilot's background.