Thanks for the shout-out! I think I mention this in the talk, but note that YMMV. I designed that benchmark as a kind of "worst-case scenario" where shadow DOM / scoped styles really show a benefit. Depending on your CSS rules, DOM size, and amount of thrashing, the perf benefit could be small to large.
Also, it's still possible to shoot yourself in the foot, especially if you have a large/complex stylesheet repeated across multiple shadow roots. (Not because of the repetition – that's optimized in browsers [1] – but rather because of the number of DOM nodes affected.)
That said, I still think the perf benefits of shadow DOM have been undersung. And Declarative Shadow DOM makes it way more useful.
Also, it's still possible to shoot yourself in the foot, especially if you have a large/complex stylesheet repeated across multiple shadow roots. (Not because of the repetition – that's optimized in browsers [1] – but rather because of the number of DOM nodes affected.)
That said, I still think the perf benefits of shadow DOM have been undersung. And Declarative Shadow DOM makes it way more useful.
[1]: https://github.com/whatwg/dom/issues/831#issuecomment-585489...