I would advice reading the "efficient rails" book, which explains a lot about how to debug RoR apps.

The fact that you have to read a book and break out a debugger to do the equivalent of "find all" in any other languages should tell you something right?

My experience is exactly the same as Milch's. I've tried to fix stuff in Gitlab but given up when I couldn't even find where it things are defined.

That can happen in other languages, e.g. Rust or C where macros are used. But it's pretty much the exception there whereas in Rails it seems to be done by default.