My advise would be to demand that they eliminate asymptomatic GCA. I have a similar story and I kept telling my Rheumy that something else was going on and it was - it was Giant Cell Vasculitis. I could taper down but within a month the pain was back and it always seemed more severe than before. PMR normally runs it's course in say 3 years - and yours and mine did not. I never had a single cranial symptom that would lead a doctor to test for GCA. I had a PET Scan that showed it. I finally went out of state to a major medical facility that routinely sees difficult to diagnose patients to get some action.
Clearly you should be concerned that you do not have something else, possibly in addition to PMR, and whatever the other is could be doing silent damage. This is true with me and I am now dealing with some of the other problems due to untreated GCA. Remember PMR is a default dx, there is no test that can confirm or deny it. It is Dx simply by elimination and so ask them to eliminate GCA. If they are resistant, get a 2nd opinion.
Interestingly my Rheumy at home is not totally onboard with the diagnoses but is willing to treat as recommended by the out of state doctors. I don't know who is right I simply know that I feel more like pre-PMR days than I ever did while on prednisone alone. Getting a second opinion is not only your right it is appropriate when you think that you are not receiving the care you deserve. I had my first PMR symptoms April 2019, pre-Covid.