Genuinely to answer, Rails offer much richer environment, Express is pretty much bare bones server, Flask is comparable to Sinatra, the only comparable thing is

Genuinely to answer, Rails offer much richer environment, Express is pretty much bare bones server, Flask is comparable to Sinatra, the only comparable thing is Django and, especially in new version it got much better, I still think Rails is much more flexible solution, which offers you a lot already premade stuff, with your ability to control how things will be used, still quite significant. Most of all, I believe a set of good practices enforced or encouraged with Rails is what distinguish it over all other frameworks. Most difficutlty with Rails is after few years when you need to upgrade, I feel a lot of busy work has to happen then.