That's all good and well, but at the end of the day, when you're being paid to fly someone else's machines, you fly them how they want you to fly them (caveat that with 'as long as it's safe).
You don't know it's 'safe' unless you know how a piston engine actually functions and what the various controls actually do to its innards.
The blissfully ignorant are generally only 'safe' because most GA piston engines are engineered to take a lot of abuse. Those who run GA piston engines on the basis of data and knowledge are 'safer', because they aren't exposing the engine to unnecessary abuse.
But Lumps: You were a little naive in believing that an employee from a manufacturer would know what he was doing, given some of the demonstrable rubbish published by manufacturers.