Your arguments are what makes landing pages be fast. It’s still not enough to push for the SaaS internals to be fast, or really any other page not related to conversion.
For those who aren't familiar with Chrome User Experience, Chrome collects website performance data while you browse under certain circumstances (I think you need to be opted into sync) and so Google essentially has detailed RUM data for any web origin with a decent amount of traffic.
[1] https://developers.google.com/search/blog/2020/11/timing-for...
[2] https://developers.google.com/web/tools/chrome-user-experien...