It's usually the upload speeds that are the bottleneck. When the upload is only 10 Mbps any video upload or large file upload will saturate the connection. In addition to having to wait for the video to finish uploading, if you don't manually rate limit the upload job speed or have anti-bufferbloat measures deployed any concurrent voice or video calls will suffer. During Covid shutdowns four people video chatting at once was no longer far fetched.
The scarcity of upload speed is why I learned how to setup OpenWrt's SQM feature, and upgraded to the highest package my ISPs offers.
Interesting. Yes, I guess the upload speed definitely matters, which cable/DSL don't provide.
I myself have fiber, and speeds are much less than 500 Mbps, but symmetric (with likely maximum two people using video calling at a time), so haven't faced that issue.