It would take me many days to create and test an admin with multiple objects, even a simple one, and then I have to maintain it. I install rails_admin and I've got what I need. This is for internal testing and maintenance. I don't care if it's heavy.

I suppose your logic makes sense if you're gainfully employed, but I bang this stuff out for myself and clients. A 90% solution with one line of code sure beats weeks of work.