I think PMR was the correct diagnosis when I was initially diagnosed. However, I clearly had other autoimmune disorders before PMR was diagnosed. Those other problems didn't magically disappear after PMR was diagnosed.

Multiple things contributed to not being able to taper off prednisone for 12 years. My rheumatologist maintained that PMR was my "primary diagnosis" but also said I had a "full range" of other problems and it would be impossible to adequately treat everything.

I would agree targeting the IL-6 pathway was the correct pathway to target since I was able to taper off prednisone.

"Dysregulated persistent IL-6 production has been demonstrated to play a pathological role in various autoimmune and chronic inflammatory diseases."

IL-6 has been implicated in PMR/GCA but those aren't the only autoimmune disorders that IL-6 plays a role.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3491446/#:~:text=Interleukin%20(IL)%2D6%2C%20a,autoimmune%20and%20chronic%20inflammatory%20diseases.
Sometimes it seems like treating a specific autoimmune disease and only focusing on one diagnosis isn't the best approach. Targeting the primary inflammation pathway rather than a diagnosis might be better.