I'm not using Cursor at the moment, but when I did (not too long ago) my experience was similar. Plan with Opus, implement with Composer, clean up with Opus.

Composer did a competent but not amazing job with a good plan. What I really liked though is it was fast! Opus could take 30 minutes to do something Composer would get done in 5-10 minutes. Of course the output wasn't perfect, but that's why I'd do a cleanup pass using Opus or Codex.

It's all a balance though, constantly changing and completely dependent on the problem you're solving. I just remain flexible and adapt my process to what's working best in the moment.