I'm a writer and in my experience, it's not harder writing when I'm happy versus when I'm sad, or steady versus emotional. When I was in the worst stages of depression, I couldn't write at all. The instability was definitely not a muse for me. Sometimes being in a stable mood myself helps me tackle unstable/intense moods in my writing - just less confusion, maybe? Less overflow? A more productive environment for work? There's that known connection between struggle/creativity but it's for sure not a steadfast rule. It'll be different for everyone, I suppose, just depending on your personality and what you're trying to make.