Again you're not making any sense at all. Apple did not provide the labor. They did not hire the technician and they didn't get paid for the technician's work. Therefore, the people who made a profit on the labor should cover any labor screwups out of their margin.
If any damage is caused by the worker, like they damaged your logic board changing a screen, then you have a valid claim on repair shop, not Apple.
Again, this is exactly the same on cars. If you have a repair that you paid for, any warranty on the work is between you and the dealer, not you and the carmaker.
If you take your logic to the conclusion, we should sue a doctor's medical school for any malpractice they do.
Do you think an entire device’s warranty should become completely nullified the moment a 3rd party touches any 1 component on a device?