It can be difficult bordering on impossible to find a trustworthy independent mechanic. Even an honest one is not necessarily going to be able to be as thorough and have the attention to detail that the owner might. And even though they are faster, they also have to spend less time than might be optimal.

I have a 30 year old car and there are one or two specialists in my city that people recommend. One of them told me I needed an engine rebuild due to an oil leak, when it was actually a specific seal that was relatively minor to replace, and the other correctly diagnosed the problem, and apparently fixed it for a reasonable price, but insisted the oil I was using was too thin, and when I deferred to their expertise, they put an even thinner oil in (I found out later) and lied about it...maybe because they thought I would come back with more leaks...so the only local mechanic I currently trust is a dealer that will work on classic cars and they charge a ridiculous amount.

So, comparing cost and expertise and tools is kind of missing the point. I would always take a new or newish car to a dealer. I have no idea how to find a decent independent mechanic, and I've tried quite a few over the years. If it takes me several times as long to do something, it doesn't really matter if that's my only practical way to get it done right.