My and my family's experience has been that if you have a good recommendation and a reliable mechanic, that's awesome, and we never used to use the dealer. But as things become more and more expensive and less profitable to even have a mechanic shop, as well as cars getting more and more particular, they can be hard to find.

Similarly, dealer's mechanic shops can be reliable or not and it depends a lot on recommendations and experiences. For example, here I go to the dealership and they have done some things for free and even said I should go find a muffler shop to fix a tailpipe hole because they would do it faster and charge me less. Otoh, it costs more money sometimes for parts.

It can be harder to get good quality aftermarket parts, sometimes, now. For one thing, there are fewer suppliers and parts makers, and that whole effort to get rid of all the old cars for the environment took away a reason for there to be parts for older cars, or sources for them. We had totally gotten junkyard parts in the past and I wouldn't feel comfortable doing that, now.

My sister still has a reliable mechanic in Ann Arbor and I'd go to him if I were there. He's getting old, though, and it's a good question whether that shop will continue to exist for how long. Maybe he'll get someone younger in and it will keep going for decades. That would be nice.