Sorry for your experience with the transition Greg 
I would like to note a few things:
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Your project uses extension modules so it doesn’t yet work in that case, but for all others Hatch provides a single command that can port automatically which is one of the reasons adoption has been so rapid
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I also view the config settings flag interface to be poor UX, so similar to PyArrow, Hatchling just uses file-based config and environment variables
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I don’t have time to advocate for this until next year with Henry Schreiner when he has more time to spare (teaching obligations) but I plan to again push for the approach taken by extensionlib. For more context see the discussion I opened for Maturin.
Basically, there are components that produce extension modules and components that pack files into an archive which we call a build backend. These are two distinct pieces of functionality and my view is that there should be an API that allows backends to consume extension module builders to find out where things got created and where they should be shipped inside archives.
As I mentioned in Discord recently, I am confident that this is the correct approach and the people that are saying otherwise are doing so because of my inability to express to all audiences why it is the correct approach.
Next year I plan to push very hard for this and get it implemented in at least 2 backends to concretely show the benefits. Then will come a PEP.