Try this instead

https://metrics.torproject.org/

The document you found is probably dated 2014. A lot of the old tor docs are still online.

I watch 1080p streaming and on demand video all the time. No problem.

I watch YouTube in HD via pipe over tor all the time. No problem.

Maybe 10 years ago it couldn't handle it. When it was all basement rigs.

There is high volume investment in nodes from a large number of companies and organizations.

My current connection speed test result is ~50Mbps. Using bridges. To an exit node in the US. More than fast enough for HD streaming.

If I find a node that isn't fast, I change it.

Another thing: there are other 'dark web' protocols and services, not just tor.