@catartist
So glad you have a physiotherapist - hopefully they can advise you in the world of RA. we liv e in a backwards world, where we must move to keep muscle strength around our joints, with a condition that screams 'don't move!"
Your doctors are being truthful when they can't tell you what to expect. each person is unique, and just how much improvement or strength is an unknown that only you can discover.
Many years ago, after a serious accident, i was in physio; doing baby steps for a long while. After about two years, my doctor told me with a big smile, that they initially, had thought I had "had it!", and never had expected me to walk again!!!
So glad they kept that to themselves.
So keep on going, don't be limited, or discouraged.
Doing physio exercises can only help.

Prednisone long term can cause steroid myopathy but I would urge you to consider other possibilities. A muscle biopsy may be the only way to be sure. I have been on prednisone for over 30 years and my Drs never considered any other cause for my muscle weakness and atrophy until I became wheelchair dependent and insisted we look further. I was on placquenil over 25 years as well. A muscle biopsy at Mayo Clinic showed neuromuscular toxicity from the Placquenil!
After stopping the drug and not improving, I was then diagnosed with CIDP, a form of Guillain Barre Syndrome mentioned previously. All the while all my Drs urged me to reduce my prednisone, which was the opposite I needed for my RA, SLE and CIDP. They made me feel guilty for taking it, but it was the only thing keeping me going. So it’s never simple and one must have facts, not assumptions of what is going on. Good luck.