In partial defence of dealers.....
Two issues affecting dealers are that firstly, they receive a very low rate of remuneration for warranty work, and secondly, they receive NO remuneration at all for their time and work in diagnosing a problem. If they spend hours chasing down a problem, another hour preparing the report to the factory, then ten minutes fixing it, they are paid for the ten minutes, and at a low rate.
So dealers are "expected" to know instantly what is wrong with a vehicle. Sadly, it doesn't work that way.... and never will. And believe me, the "technicians" at the factory are mostly just as much in the dark.
The combination of this and the factory attitude creates the almost universal trouble with warranty difficulty with ALL vehicles.
If you read your warranty carefully, you will probably find that the definition of warranty is "the replacement of faulty parts."
Think about that.
So it can easily boil down to how much time and expense the dealer is prepared to donate to (a) his customer and (b) the factory.
Been there, done that... 25 years of it.