That sounds almost like the complete opposite of my experience and I'm also working in a big Rails app. I wonder how our experiences can be so diametrically different.
What kind of things are you using it for? I’ve tried asking it things about the app and it only gives me generic answers that could apply to any app. I’ve tried asking it why certain things changed after a rails update and it gives me generic troubleshooting advice that could apply to anything. I’ve tried getting it to generate tests and it makes up names for things or generally gets it wrong.