For many autoimmune conditions, prednisone is used initially as a "bridge" to treatment with a biologic. Prednisone works quickly while waiting at least 3 months for the full effects of the biologic. Possibly ... the biologic might not work so there could be a 3 month delay in being treated.

For GCA, the risk of losing one's vision is a distinct possibility while waiting for the biologic to work. For PMR, the pain typically is just too severe not to start prednisone.

By comparison, when I took 60-100 mg of prednisone for uveitis, it was also to preserve my vision. The difference was that I could taper off prednisone in a couple of weeks. Remission was sustained until the next flare of uveitis. My case of uveitis was very responsive to prednisone and I didn't have to take prednisone very long for a "sustained remission" of uveitis.

Invariably the next flare of uveitis was a year or so later. I don't think biologics for uveitis existed 35 years ago. I gained so much experience with tapering off prednisone that my ophthalmologist documented that I was skilled with prednisone tapers after more than 30 flares of uveitis.

The uveitis specialist wasn't impressed with my ability to taper off prednisone. She said I should have started a biologic years ago to prevent the uveitis flares from recurring so much.

Exactly

The following link says the following:
"A patient may notice a decrease in symptoms as soon as 1 week or as long as 12 weeks after starting a biologic, and symptoms may continue to improve for months afterward."
https://www.arthritis-health.com/treatment/medications/biologics-basic-facts-patients#:~:text=Biologics%20Take%20Time%20to%20Work&text=For%20example%2C%20many%20people%20who,develops%20antibodies%20to%20the%20drug.
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The above link also says:
"A biologic drug targets and prevents a specific reaction from happening, stopping the inflammatory process in its tracks. In contrast to biologics, conventional drugs treat general inflammation (and resulting symptoms like joint pain) after it has begun."
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My experience with Actemra was the same. It was unclear to me how fast Actemra worked. I was on 10 mg of prednisone when Actemra was started. My rheumatologist said that I needed give Actemra 3 months to see if it would work for me.

I was used to tapering by 1 mg per month so that was how I tapered from 10 mg to 7 mg. It took 3 months to taper to 7 mg just because that was how I usually tapered. My pain didn't increase on 7 mg. My observation was that Actemra "seemed to work" but I didn't know if it was working or not. I didn't have a flare at 7 mg and didn't need to increase my prednisone dose was all I knew.

My assumption at the time was that I should be able to taper faster IF Actemra was working. I decided to test my assumption and tapered by 1 mg per week from 7 mg to 3 mg. Actually, I was getting impatient and I wanted to get the "inevitable flare" over with.

I was getting misinformation about fast tapers and that it was safe to take 5 mg of prednisone for the rest of my life. The "experts" on another forum said doctors in the USA were "breaking the rules" by treating PMR with Actemra. This was in 2019 so PMR being treated with Actemra was unconventional at that time.

When I got to 3 mg without a flare, I was nervous (more like anxiety) about tapering so quickly. I felt okay but I was conditioned to think that I shouldn't taper off prednisone so quickly.

I saw an endocrinologist about 2 years prior to this when I was still taking 15 mg of prednisone. She said there was nothing she could do if I still needed that much prednisone. I remembered the endocrinologist telling me if I ever got to 3 mg that I should come back to see her.

I told my GP that I was unsure about what to do. I mentioned to my GP what the endocrinologist told me and that prompted him to check an a.m. cortisol level. My cortisol level was low so I was told not to taper any lower than 3 mg.

It took at least 6 more months for my cortisol level to improve. My prednisone dose hovered around 3 mg for months because of adrenal insufficiency. As far as I could tell Actemra was working for PMR but I had some "discomfort" because of adrenal insufficiency.

Two time cancer survivor here. No biologics for me, the risk is too great. I have 3 diagnosed autoimmune conditions, including PMR.