Careful giving definitive advice based on one cell phone photo.
If you correct only the area under the door handle, will it make the adjacent areas look that much worse?
"You could get about 75% of it out with very little material taken off from what I can see."
How can you tell?
"From what I can see" is the the operative phrase. from that angle, it looks as I described. However, he can see the car from all angles. If the peel looks deeper than that from other angles then he has the advantage, and needs to be more cautious.
As far as the quarter looking worse after he does the door, to ME, the door looks worse right now, so doing the door will make them look more even.
If this is to be done at all, it should not be sanded down to the deepest valleys of the peel. The high parts of the peel relative to the valleys are what bothers, so if one is very conservative and stay far away from the deep parts, I think improvement could be made at rather moderate cc loss.
Perfection is unrealistic here but a small improvement seemed to be what he was looking for based on the thread's title.
As I said initially, I don't think that sanding factory clear is practical. What if scratches happen later and you would really need that greater thickness to sand down to remove scratches?
Paint needs to be a certain thickness to have longevity, and factory paint tends to be thinner than show car's paint.