Well, you’re dead wrong in your logic. Labor manuals are a GUIDE and not etched in stone. There’s no law that even says any shop has to use one at all. They can charge 4 hours per if they want to.
Maybe you would prefer that a mechanic bills actual time and instead of spending 1.2 on a strut they could easily spend 3 hours per side while loitering around the coffee pot and bill accordingly.
There is a lot more to that 1.2 hours mentioned than you could even dream of.
It’s probably useless to try and break down how the flat rate system works because it sounds like you have your mind made up already. If you were involved in actually working in the system and knew anything about it you might have a different outlook on it.
This is especially true at new car dealers where mechanics have to wrestle warranty times.