I was a licensed auto mechanic (technician) for many years until a work related injury forced to me to change professions. I can say, from personal experience, that it’s a tough job, especially diagnosing electrical problems, such as a broken wire within a wiring harness that may contains up to 100 wires.
As for “book time”, that’s called flat rate. A good tech can beat the “book time” due to his knowledge, ability, and the $30,000 worth of tools he bought.
Don’t knock the Techs, on the whole they do a great job.