That's true! Whenever I got test the speed of my internet, my WIFI goes up to 100mbps, but when I watch videos and stream on YT, it buffers a lot of times. Maybe because my router's kinda old? I'm not so sure tho.
I think Facebook has too many features now as compared years ago. Before, it's easier for users to navigate the app or the site. Some people are also migrating to other platforms.