On my home network, I have the following:
Speedtest.net: 250+ down / 800 up
Home Asus router: 800 down / 800 up
Home Google mesh run off the router: 800+mbps 800 up.
Logging into century link (I use centurylink fiber) shows: 940 down and 800 up.
We have all the streaming we care about with movies and so on, so again, I don't have any issues. It's just a curiosity.
What could explain that difference between online speedtest and local versions of the same thing?