I agree. I thought the same thing after reading the essay. That the shades are cognitive shadows, so their formation could cause a perpendicularity. Also, it was mainly because there was this undertone that the perpendicularities were dangerous and shades are one of the most dangerous thing on Threnody. (Not including the Evil, but that, I think, is Fainlife. Someone wrote a theory on it in 2017. And if you consider that Uli Da was Fain, it makes sense.)
This could be nothing, but I also, I often wonder if the shades embody the opposite of Ambition:
--- you need to walk and not run --- you need to use the same old fires and not go making any new ones --- you cannot go around killing anyone
In other words ambition is dead on Threnody because Ambition is dead on Threnody. --Kind of poetic, but without any overly logical explanation. All I have is that "the waves of destruction—carrying ripped-off chunks of Ambition’s power—twisted both the people and the planet of Threnody." And then all I can think is "Ambition's power... twisted".
One more idea: If the Evil is Fainlife, that could be Ambition or Uli Da's army. And then, the shades could be the army against Ambition, which could explain their intent...
Shades are the the enemy of Ambition.
Any thoughts?