[runako]

> The user would like the website to have native scroll physics, respect their system preferences, react to changing window sizes and with different input methods, screen readers and so on.

Yes, these are features implemented by every popular browser via HTML & CSS. Fancy front-end work frequently breaks these features.

> key to a good user experience was server side control

I think you're reading my comment from an extremely front-end perspective. I simply mean that where possible it's better to render pages and do logic on the server side versus on the client side. The same HTML + CSS is generated either way, the only question is what % of the work is done by the user's device vs what % is done in a data center.