So I inherited a 5-year+ Rails app having never touched it before, and having spent two years dragging it from version 4 to 7 I actually get the hype. Everything I want to do for a boring REST app is already built in. Side-jobs, live-updates, ORMs, it's all there.

Would I use it for a new app, yes. But it is very opinionated, and the tools take a while to get working nicely.