Heads up, according Chrome Dev Summit talks/slides looks like in January 2020, Google Lighthouse v6 will be released so Google PageSpeed Insights v6 will be out too. They are adjusting the weighting and adding new metrics for the Pagespeed score - moving First Contentful Paint (FCP) to a higher weighting than it has in Google PageSpeed v5 and also adding a Total Blocking Time (TBT) and Largest Contentful Paint (LCF) metric https://twitter.com/bunopus/status/1193999246812278784. Both First CPU Idle and First Meaningful Paint (FMP) metrics are being removed.
This also makes sense with Google Webmaster Console adding a new Speed Report which also evaluates and displays page speed based on First Contentful Paint (FCP) and First Input Delay (FID) https://webmasters.googleblog.com/2019/11/search-console-speed-report.html
Actual Google Dev Summit 2019 Youtube session that talks about this is here.
According to data compiled by Web Almanac 2019 By HTTP Archive, First Contentful Paint (FCP) metric is highly influenced by the type of device (desktop/mobile), ISP connection speed and geography.