I'm not sure it is that comparable, and agree with domalino on this one. Thought the same myself earlier.
It taking a really long time as it goes through various courts, I can get. It would be expected, civil servants time and availability, general caseloads and commitments to things already in motion, waiting for its turn, on top of then the time it takes to review it and rule on the matter.
A panel, assembled purely for this purpose with no other commitments should really only take as long as it takes to review the information and come to a conclusion.
You are right in that the PL took 4 years, but in some ways you'd think there would have been a wait while the uefa investigation and then the cas process took place too. And even if not, if they were actively working on it for 4 years, doesnt mean it takes the same time to review it.
The cas review of Uefa's decision on took months. Uefa's regulatorybbody that dishes out punishment took months, once the charges were put forward. The one that took time was the investigation to come to the charges. I don't see why the regulatory panel decision part of this should take as long as many think.