Scott Jehl argues that performance metrics such as First Contentful Paint and Largest Contentful Paint don’t really capture the full picture of everyone’s experience with websites:
These metrics are often touted as measures of usability or meaning, but they are not necessarily meaningful for everyone. In particular, users relying on assistive technology (such as a screenreader) may not perceive steps in the page loading process until after the DOM is complete, or even later depending on how JavaScript may block that process. Also, a page may not be usable to A.T. until it becomes fully interactive, since many applications often deliver accessible interactivity via external JavaScript
Scott then jots down some thoughts on how we might do that. I think this is always so very useful to keep in mind: what we experience on our site, and what we measure too, might not be the full picture.