>I'm sorry, but saying that as long as your process isn't broken (whatever this means) and your system isn't poorly designed then Rails is maintainable seems to be a pretty weak argument

If you've got a dysfunctional team and poor design, the language/framework choice isn't gonna help you. There isn't a framework in the world that will save you from tight coupling, lack of styleguide, business logic scattered all over the place, poor test suites, or monoliths made by bootcamp graduates.