Are RGB and HSL color models all broken and useless? Yes, I know their limitations. But of all graphical software I use daily. only GIMP supports LCh, and using it is pretty unintuitive.

I see how position-anchor and stuff are coll for complex layouts, but they have poor support on low-power mobile browsers, and, frankly, are not that useful for a minimalistic CSS framework. If you want complicated layouts with non-obvious anchoring rules, you're not the target audience.

Cascade layers are very useful for complex designs with many independently added stylesheets. They would be great to have. OTOH again, if you need this level of complexity, you're likely not the target audience of a pico-sized CSS framework.

I would say that a minimalist framework should make judicious use of CSS3 features, and not try to be excessively clever. In reliable engineering, being smart often means avoiding being clever.