I reckon every app I’ve every worked on, with a registration section, someone has suggested to build a form-engine and where they weren’t persuaded out of it, it has always ended with it having to be stripped out

100%.

I think of building an unneeded form-engine as a rite of passage for moving beyond being a junior developer - you have the technical ability to pull it off but not yet the know-how to realise that you are about to let yourself in for a world of pain