IME Rails codebases are a few months with a mediocre team or a few bad choices away from becoming an absolute garbage fire, and all the magic in Rails is part of why even a little of that sort of activity does so much damage.
Amazing for starting from scratch solo or with a very small team. Dangerous (mind: not necessarily bad, just dangerous) under basically all other scenarios, including ones that that sort of ideal situation might develop into. In particular, a great deal of discipline and excellent taste is required to maintain the kind of legibility and reliability other languages & frameworks can give you "for free".
I expect a Rails project has the best hope of remaining good at a business that's got solid funding for an in-house team from day 1, and has good retention for that team. However, lots of startups or experimental ventures by larger firms experience a lot of thrashing and turnover in the early days, and often go through one or more periods of heavy outsourcing, while also being the kind of resource-constrained enterprise for which Rails is extremely tempting.
Arguably Rails is still the right call for them, if it gets them to market fast, but those kinds of places consistently end up hit with slow, expensive, risky feature development just as they're starting to get traction, much earlier than the usual "eh, needing to replace this will be a good problem to have" phase, and part of that's because Rails falls apart so fast if you color outside the lines at all.
