A good instructor is not a good charter pilot. They become too institutionalized in the flying school doctrine.
They will become a good regional/airline pilot, but certainly not good charter pilots.
A good instructor with experience often makes for a good charter pilot but a good charter pilot struggles with instructing
What a load of crap from both sides of the argument.
It doesn't matter where you have flown and what you have been doing. There are many great charter pilots (ex-instructors), great instructors (ex-charter pilots) and then there's sh*ithouse instructors and charter pilots from varying backgrounds.
It really depends on the persons' attitude and their ability to adapt to whoever they're working for.
I get the impression that purist charter pilots or purist instructors are just defending their own turf (or percieved inadequacies). The arguments only tend to come from pilots who have only worked in one area and not the other.