His criteria are subjective, yes, but isn't that the point? The point of music recommendation engines isn't to figure out the absolute "best" playlist based on a starter song. It's to figure out the best playlist
for the individual user. If the user is asking "WTF?" about the songs on his list, then by definition, the engine has failed that user.
While the author could have been more objective about his criteria, ironically enough, I think he missed the more salient point that he raised by implication: that music engines should be mapping the user's behavior patterns vis-a-vis the songs in his collection, and not so much objective connections between songs. This is what Genius does and has always tried to do, and it's why Genius seems to work better for the author. Genius doesn't focus as heavily on attempts to forge objective links between songs, so much as it focuses on attempts to draw links in behavior patterns w/r/t songs by likeminded users.
When listening to songs in a collection, our brain maps out its own connections between songs, as reflected in the way we compile our own lists consciously or subconsciously. Sometimes those connections make objective sense (i.e., "I want to listen to '70s funk, so I'm going to pick ten '70s funk songs in a row."). Sometimes those connections make little objective sense (i.e., "I am listening to a track by Lady Gaga, and afterward, I feel like listening to a track by J.S. Bach."). A good mixing engine figures out the idiosyncracies and subjectivity of our brains, as reflected statistically by the choices we've made in the past.