Well the 8361A is arguably the best speaker in the world for distances from 1 to 4 meters. So yeah i feel the skepticism is very warranted.
And Sonos might be the largest speaker company in the world by market cap. Sonos makes nothing but audio and their market cap is $2B down from $5B before the current stock market crash. Literally, Sonos only makes speakers/amplifiers/streamers and they're $2B. That's a lot of weight to throw around with your suppliers.
The Sonos Five is $550 and made in either China or Malaysia depending on product revision. Cost of living in Malaysia is 1/3rd of Finland, so you'd assume that the same Sonos Five made in Finland would be $1650.
Now imagine that the OP is listening content with minimal bass. Let's say an acoustic vocal with no background music.
Above 320Hz, the Genelec is now just a 5" woofer compared to the Sonos Five's 3x2.75" = 19.6 sq inches vs. 17.8 sq inches. It's probably easier to control distortion with 3 small woofers as opposed to a large woofer.
Now look at the photo of the OP's setup. The Genelec's are pretty high up whereas the Sonos is closer to being on axis. The OP is running them horizontally so that actually increases dispersion (as opposed to running the Sonos Five vertically).
Last, consider the author listening to lower SPLs where all of the engineering behind the Genelec is wasted.
It's a very stacked comparison, and by no means do I think the Sonos Five is better than the Genelec. However, I do think the right (or wrong) content can easily make the difference smaller than you'd think. I also think the Sonos systems punch way above their weight when setup properly. You give up a lot of audio quality for a gain in a lot of convenience.
This only works at lower SPLs.