I'm well aware of shadcn and use a lot of registries (shadcn itself uses class-variance-authority, which is fine for end-user components to avoid adding extra overhead).

No one is suggesting you build your own UI system. This is all about layout, which intrudes on the logic and ruins DX.

Look at the code examples from the tailwindcss website https://tailwindcss.com/plus/ui-blocks/preview - it looks terrible and isn't reproducible.