You sound like you've never heard of the independent mechanic that as far as I can tell
You sound even worse. An independent has to specialize in a topic, like transmissions. Would you trust him to work on the cars computer system? A dealership say Ford, has to be able to work on all aspects of fords, same with gm, chyrsler and Toyota. And stand behind their repair.
You absolutely proved him correct when you claim an independent has to specialize in a topic as narrow as transmissions. Most independent mechanics I have used have been able to work on a wide range of automobiles. There has been some very specialized work, such as with more rare hybrids like the 05-07 accord hybrid, where I have had to use a dealer in the past. But I have only had one car repair in 20 years that needed a dealer. And if dealers did not exist, the market would compensate for those rare cases in their absence.
It is funny you stand up for dealers because of their repair services, when generally that is the department people like the least at dealerships. I thought it was general knowledge to never go to a dealership for service unless your car was under warranty. They are overpriced and refuse to use after market parts.