The reviewer said: ''8K YouTube videos are of surprisingly low quality, to the extent that we felt the need to double-check that we were indeed receiving 8K (we were). ''
You guys do know that all online streaming platforms - and especially YouTube - use heavy compression on all of the content available?? Heavy video compression (on the web) is a 'necessary evil', if you will.
Phones aside, even most entry-level consumer (video)cameras nowadays have a video-bitrate in excess of 100Mbs. But once you render you video 'YouTube Ready' (which is around 25Mbs), YouTube then further down-compresses it to 10Mbs or less. That's a fraction of the original 'crisp-looking file'. :
So, when you're watching content in 4K or 8K on YouTube (in particular) you're getting 10Mbs (on average). It even drops down to 6Mbs in a lot of cases (i.e. content). 100Mbs vs 10Mbs? Let alone 500Mbs (the bitrate used in the professional world).
In short: 8K resolution needs higher bitrates in order to show its full potential, and that's something the World Wide Web is not ready for - and won't be for years to come. Not even physical media is quite ready for such huge - and unnecessary - resolution.
P.S. Vimeo is more generous regarding the video-bitrate (averages around 15Mbs), and there's plenty of watchable +4K content.