Pretty sure the cases where this isn’t true are the scenarios that are impossible to create without JavaScript, like infinite scrolling. Do you have counter-examples?
Server side issues? Images being too big? Maybe slow CSS, if there's such thing?
> Maybe slow CSS, if there's such thing?
That can definitely be a thing. However JS is usually a much bigger issue.
There's a demo somewhere of infinite-scrolling without JS. The hack is you just never close/finish the request/connection so it keeps sending new content!
Recently, https://garden.bradwoods.io/notes/css/blend-modes was linked to, which, using Firefox on Android, takes hundreds of milliseconds to paint the new screen whenever I scroll. I can also notice the behavior on my desktop if I scroll quickly enough, even if I disable JavaScript. So it most likely has to do with an advanced CSS feature, perhaps the blend modes it is showcasing.