I've always assumed that making a fast and responsive website isn't a technical problem, but a social/political one.
It's easy to create a website where interactions simply fetch the necessary resources and update the DOM as required. But managers then insist on adding 20 trackers so every little click and interaction gets logged somewhere for analytics.
Of course they are. There's a significant overhead from a virtual DOM and reconciliation with the real DOM. Then there's the larger overhead from relying on JavaScript for everything. The JS VM in modern browsers is very performant, but it can't optimize poorly written code, whether that's from frameworks, the gazillion libraries modern web sites depend on for analytics, trackers, ads, shims, helpers, etc., and, of course, any custom JS specifically written for the web site.
Browsers can enable very rich and responsive interfaces, but web development is bogged down by the insane state of popular frontend stacks. There's a recent trend of rejecting this insanity (htmx, Nue, Datastar), which I hope gets us on a track where we optimize for user experience using native web technologies.
It's easy to create a website where interactions simply fetch the necessary resources and update the DOM as required. But managers then insist on adding 20 trackers so every little click and interaction gets logged somewhere for analytics.
Or are frameworks REALLY that slow?