This doesn't line up with my experience. IME these are the major drivers of web "slowness" for different types of sites: 1) Client-side-rendered apps that have

This doesn't line up with my experience. IME these are the major drivers of web "slowness" for different types of sites: 1) Client-side-rendered apps that haven't embraced hydration of pre-rendered HTML suffer for it. Not because the JS is necessarily too large, but because it blocks the content from being visible. This would be bad even with a small bundle. Luckily this is an easy problem to solve today, but not every site has done so. 2) Many public-facing sites are afflicted with marketing scripts. I've seen sites with (I kid you not) several times the amount of marketing JS (by weight) as they have actual functionality-giving JS. The actual devs often don't even have control over these scripts (thanks to Google Tag Manager), and even if they do they probably don't have a say in what can be removed. 3) Complex sites/web-based tools are a separate beast. You're not optimizing for first-visit, you're optimizing for responsive interactions. This has even less to do with bundle size, and often not even much to do with JS itself. In my experience the limiting factor on these sites is usually reflow (DOM/style changes).