But I can save a different outside from a lot of pain. For example our frontend dev won't have to worry about setting up the backend with all it's dependencies, instead docker-compose starts those eight containers (all, redis, db etc) and he's good to go work on the frontend.

If you freelance and work on different project, sure rvm is a great thing, but docker will contain it even better and you won't litter your work machine with stuff like mine is after a few years.