For rapid prototyping, I think RoR has still something to say.
I like Django but I see little use (correct me, if I am wrong) from big Startups.
I was able to setup a tiny custom status page with RoR picking a module found on the web, and starting customizing the app for my own goals.
AngularJS and React are the king on the frontend in this years, so the Django/RoR approach seems a bit "old"; nerveless on RoR guides you find a way to use RoR only as an "API" Layer, so integrating it with an Angular frontend, for instance.
And with K8s and microservices, scaling is not a big issue if you code a share-nothing stack.