"The asymmetry is in the kites shape, either because of the fabric or sewing."
Is this a measured fact or just guessing? If you knew foilholio better how kites are sewn and knew how precise used parts are and how high quality the fabrics are (they don't stretch randomly) you perhaps wouldn't write that kind of bold statements.
Show me one kite, preferably known make like FS or Ozone, which has asymmetry in its shape, "either because of the fabric or sewing." Exact measurements, not stupid guessing "it must be bad sewing work"... I remember in some kite book there was "an example" in which a rib was claimed to be sewn upside down resulting crooked flight. In practice this is very difficult to do even on purpose, upside down rib just don't fit to its place. It is about the same like to use right shoe in left foot.
"Trust me enough people know the truth about this..."
Nonsense, if you read some opinions from the internet it does not mean it is true. It is so difficult to measure kite panels precisely from the kite that most people are not capable or willing to try to do it. I am quite sure if you foilholio would go and measure kites, every single one would be asymmetrical according to your "measurements"
Resellers/manufacturers are ready to take back some percentage of kites, good or bad. These "bad" ones may be used as a school kites, resold or used as a spare parts or prop. It is wiser to them to not to start arguing with difficult customers and possibly harm their reputation.
"He doesn't even realize you can test this without sewing."
I'm not very intererested in methods of unprofessional fixes. I guess you mean using tape to make test pleats. Have a nice day with taping kite and doing test flights..
Like I said earlier it is possible to counter asymmetry by adding a new asymmetry. I don't recommend it, it is much better to fix original asymmetry, the real cause for crooked flight. Unfixed original asymmetry may increase or added fix may fail.
PL's advice to do pleats was meant to adjust primitive Pilot kite, a kind of bush fix. To jakemoores credit he did his pleats nicely.