I don’t think dealer rates are double independents unless you compare a high end dealer example to a very low end independent.
A dealer rate will be higher out of necessity as the dealer has expenses an independent is never faced with. Required specialty tools that may never be used, alignment rack/wheel balancer/whatever, training schools, the cost of a service manager/writers/etc. are a few examples.
The dealer also has to face dealing with warranty issues which are usually a money losing proposition. Warranty periods and mileage have also been extended much further than they used to be.
Labor has gone up but so has everything related to it.
For some perspective, consider the old paper I found in my attic a few years ago while rummaging for something. It was a copy of a dealer repair order for a clutch job that I paid to have done. At the time I had gone through a major knee operation and was on crutches so it was not a DIY repair .
The labor rate at the dealer in 1970 was 7 dollars per flat rate hour X a 3 hour charge and 20 something for the clutch kit for a total of about 50 dollars. Big money back then…
Mechanics were probably earning about 2.5-3 dollars per flat rate hour so the mechanic earned less than 10 bucks on a clutch job.