In the abovementioned shop, that may be true.

But. For those who have "proven" their knowledge as an ASE certified master mechanic; have access to the proper information; have the proper tools; and their brain works, I'd say they were qualified to work on just aboot any vehicle. It ain't rocket science.

Most of us specialize because it reduces our need for special tools used on other makes. Bumper to bumper familiarity with a particular model allows you to work faster with more confidence.

Many mechanics got their training through a dealership and after a period of time, they went off to independents or opened their own shops.

The world has many excellent and competent mechanics that happen to make their living doing something else. This forum is full of them. We learn from each other.