I can understand that, and I agree we are still figuring it out. In React, I find myself often separating my presentation components from my container components to start and that works 85% of the time. In those cases where I have a lot of styles (atoms), I will break that out into its own file.
I prefer CSSinJS because to me, there's less of a context switch and I haven't ran into a scenario where it didn't meet my needs.
Unfortunately, most of the tooling for this pattern doesn't support the shadow dom, so I find myself using Stencil when I create framework agnostic components.
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