I may know less, but I'm not being watched for efficiency; I'm less likely to break out an impact gun (partly because it doesn't fit under the car as easily) and I can compare the old to the new. And if I'm tired, I can take a break and check the manual.

And if I do the work, I do the test drive; and if something goes awry, I should know what to look for, for that rattle, that noise, or the next warmup. A quick lube tech might drive your car 30ft to a parking spot, and is likely thinking more about the next car than, any given noise, or whether the thermostat has cycled even once.

On your further, sure you can split the difference, and I do do that when I do take it to a shop, and most of the time I've not been impressed (though I have been with some bmw shops). But this only works if you know what your engine sounds and looks like when clean.