Figma actually now has grids: https://help.figma.com/hc/en-us/articles/31289469907863-Use-...
Figma has a bunch of good tooling, but getting designers to use it, and use it consistently, is the real problem.
Designers exist in a realm seemingly, where outside pressure can't really be put on it from an organizational level to get them to uniformly adopt a set of standards they will always adhere to. Every company I have worked at, big, medium, small, seems to have this problem
Browsers are by and large black boxes—less because of their architecture and more because of the sheer size of the code, although Firefox, for example, seems to have been moving towards a less open architecture for most of its history as well (deCOMtamination, death of XULRunner, Quantum, etc.).
What you really want in a parametric web design tool is to crack open the layout engine and the CSS cascade and inheritance, at the very least. That’s a lot of work to target a demographic of designers and programmers who by now have largely decided to ignore CSS in favour of reinventing inline styles badly (Tailwind) and insert markup as necessary for the desired visual effect. (Is there a tool to do CSS in terms of React/etc. components, with proper cascading, custom pseudoclasses and pseudoelements and so on? I haven’t seen one.)