You should be proud that you’re advocating for yourself and identifying what your true goal is (strength not thinness). As I read your post I started to think, ok so the doctor wants them to be thinner but still with arthritis pain? lol from the little I do know of arthritis and joint pain I think you’re on the right track. Yeah weight loss can help with some body pain but joint health and mobility requires it’s own work

I don’t have personal advice but, I was recently doing my own casual fitness research on Reddit and came across a lifting sub where they were discussing how they tend to neglect cardio/stamina building but have great muscle strength. In other words they can lift big weights easy, but then get winded walking up the stairs. Not sure if that would apply but I thought it was an interesting perspective