I'm halfway through season three but I am very very invested in the fears so I think I generally have a decent grasp of them. I woke up in the middle of the night in a cold sweat and made this chart:
The Eye, the Spiral, and the Web are fears connected to the mind and knowing.
The Desolation, the Slaughter, the End, and the Extinction are all related to loss and usually death of some kind.
The Vast, the Lonely, the Dark, and the Stranger are the opposite of the fears connected to knowing. The Stranger maybe seems like a bit of an outlier, but the fact that the Stranger's ritual is explicitly called the Unknowing makes me feel it belongs here.
The last group is the Corruption, the Hunt, the Buried, and the Flesh. This is perhaps a little more abstract, but these are all designed to make you aware that you are nothing more than a mammal on this planet. You are made of meat, susceptible to disease, able to be hunted and trapped like any other animal. This is also opposed to the death group, as this grouping has to do with life.
What I really would like to see is if there's a further subclassification, so that I could arrange them in a 4x4 grid. This also somewhat implies the existence of another Eye related fear, and as the Extinction is a newer fear there is precedent for this. My initial thought was something related to the weird quasi-community and parasocial voyeurism the internet itself has created. Maybe this could be what Sergey Ushanka was an avatar of. Or maybe I should put the cork and string board down and just finish the series. Either way I'd love to hear your thoughts.