I wrote a post very similar to this comment that you might be interested in reading. I broke down what takes time to load, how fast the browser determines something has loaded, and how fast the user can perceive the page loading. I ended up having to take a high speed video and measure frame by frame the time it took to load for user perception.
https://www.ireadthisweek.com/author/ireadthisweek/post/2022...
The TLDR is it takes longer than reported.