Well, a company doesn't have to be big to be impactful. What's important in my experience is a productive environment which can foster the occasional side project.

This is actually something that I've struggled a bit with, because it feels like the most interesting and educational jobs are the ones that involve more than 40hrs/week.

Sometimes I wish that I could find a 20hr/week role with the potential to make big positive improvements in peoples' lives. But there are always other groups trying to do the same thing, and they're never happy to stop at part-time.