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.
That is absolute horse****.
Where I come from, many, many airline pilots have successfully transitioned from extensive single pilot IFR operations in high performance piston and turbine twins into multicrew jet airliner operations - it is
not rocket science.
It is far easier for a pilot with extensive single pilot experience to transition to jet multicrew ops, than it is for a magenta
wunderkind to revert back to raw data/ basic instrument flying
sans automation when things go off the rails.
Experience, eh! Who needs it?
