QUOTE<Flying privatly Cessna/whatever piston for a prolonged period (over 5 years let's say) often makes pilot no longer suitable for airline environment, because along with raw flying skills (good) he also getting adopted to single pilot, light aircraft, VFR etc. Very recently we had to say goodbye to FO with as much as 4000 hrs SEP (and very good background references), after struggling for 300 hours on the right seat of airliner it become clear he cannot adopt and follow CRM, SOP, performance calculations, situation awareness in congested terminal areas etc, while most of our 300 hrs TOTAL time young FOs have absolutely no problem with it.>QUOTE
I'd take exception with the term "often". I've found in a fairly long career that "often" it's just the opposite: some of the best pilots came from a single pilot background...but I must say that most of them had extensive single pilot IFR experience flying light twins and singles in night freight. A GOOD pilot can adapt to crew ops easier than a BAD pilot regardless of his experience level. Perhaps some of those that were washed out were simply not good pilots, never mind their flight hours. The guys flying single pilot night freight (yes, it's IFR) without autopilots or glass cockpits have unmatched situational awareness and flight skills and have proven it by surviving. I'm not sure what performance calculations have to do with low time.
I wouldn't say low timers are inherently bad pilots, but chances are they won't display the SA or skills of a more experienced flyer.