If you live near philadelphia, there must be hundreds of shops that work on vehicles.
Dealerships do not have all the best mechanics. Alot of great mechanics leave dealerships for the same reasons vehicle owners do not like dealerships.
Find a shop with certified mechanics. Have all the cylinders checked with a compression gauge. The reading of one cylinder is not a good idea, because the compression gauge could be faulty.
If in fact cylinder #4 reads at least 100 psi, I agree with old school that further diagnoses is needed before condemning the motor. Was anything besides the spark plug replaced? Wire, coilpack issue or something else could cause the motor to run rough.
An engine with 100 PSI on one cylinder is never going to run right and will have a rough idle.
Without diassembly and a thorough inspection of the head I fail to see how they can state that you need a new head. It has to be very bad to get to that point.
With a 100 PSI it’s damaged goods and needs to be repaired or drive it to the bitter end.
It is not your fault that things are not adding up. What I mean is, if there is “valve damage” that is visible with or without a borescope there is no way that the same cylinder could show 100psi on a compression check.
I don’t know what “only loops inspect” means so I can’t expect you to know. If you are set against seeking another opinion, well then you are stuck accepting the bottom line of this one, even if it is not clear how they got there.
I could give you a list of 3 or 4 things you could ask the Dealer to clear up, if you wish.