Wilshire, it seems we have a defining quote: "The Gnosis is simply what the Anagogis could be if the proper conceptual leaps were made" - which states an evolutionary link between two magical paradigms. All we need to consider is a factor of a nonmen participation, a true reason of that short "if".
Maybe, nonmen tutelage was just a time-saver which gave halaroi a new branch of sorcery a few thousand years earlier. Maybe, nonman's cognition is truly alien and acts as an essential ingredient, so halaroi by itself are limited to the forms of anagogic sorcery and, if they are too lucky, they can comprehend and repeat some gnostic explanations of Gin'Yursis.
First variant states for Kellhus ability to reinvent Aporos on the fly, because he was clearly making scientific breakthroughs while just listening to Akka's teachings abouth common math, logic etc. Second variant states for a bridge where even Aspect Emperor shall not pass. No halaroi allowed, lol, even if they are tweaked ones!
As for myself the second options looks more real. Two thousand years passed but there is no big signs that "conceptual leaps" could be made through pure human efforts. And we're talking abouth Scarlet Spires here. About few-hundred-year-old-mageocracy with tremendous intellectual power, who knows the overall direction of research.
So I can only guess what halaroi lack to invent gnosis and/or aporos by themselves. After all, cunuroi were a long-living specie with a lifespan about 400 years even before the inchoroi. Maybe it's just a difficulty of culture transmission & accumulation? One mortal cunuroi philosopher is equal to a sequence of 5-10 mortal halaroi adepts of a certain philosophic school, who will have to study their predecessors reflections and to live under a constant chance of extinction even before making their first worthwhile discoveries. Cunuroi is just a better basket for knowledge. :c

A second thought. Do they use aporos to make anarcane grounds or it's a meta-aporetic level of intervention? The most famous anarcane is Athrithau, located on the far north and near Ishterebinth. A former cunuroi lab, abandoned after ban on the Aporos?

A third thought. They should have some apotetics or meta-aporetics nerds in Min-Uroikas for anarcane is the opposite of topos. And it's generally a bad idea to be horribly damned and at the same time to live right somethere, where curious ciphrangs can just pop out of the thin air and grab your ancient consulty ass.

The no god was destroyed by the heron spear

Actually, as a consult fanboy, I hope that No-God was not destroyed, but launched. Like the carapace was less a body or an armor and more a mobile launching pad or a sort of metaphysical egg. That's why there is no "first" or "second" apocalypse, there is just apocalypse and it's purely successfull phases. >:з

to make them more like Tolkien's elves

... and now I can't help but compare dunyain & mangaecca with numenorians.

If Erratics need elju to keep them tethered to the present, then who is filling this role for the Nonmen in the Legion?

A fellow Nonmen. :3

What would make it impossible for them to see paintings? Can they read writing, then? I can't think of any reason why anything with sight wouldn't be able to "see" paintings.

As far as I remember, percieving a flat illusion of a volume is a trainable skill, it's not inherent even to the people. Where most of current human population get this through early childhood (along with zero language, walking and other base stuff for a tiny drunk adult), there were tribes of primitive people found only in 20th century who lived with a very scarce material culture. That certain circumstance prevent them from both creating such illusions and training in recognising them. It seems a window of opportunity here is quite wide, because even adults developed that skill with a help of a pictures brought with explorers.

And we know cunuroi & halaroi have some deep diffirence in perception. Like, cunuroi look exact the same to halaroi, but manage to differentiate between themselves with no problem. I hope that wasn't a "all europeans look the same to asian et vice versa"-joke thrown in by Bakker. Though it would make a damn good dark humour in context of nonmen memory difficulties.

Are we all in agreement we expect it to be the worst Topos in Earwa? The mostly thinly seperated place from the Outside?

My mood is rather consulty & unholy, so please let me suspect Min-Uroikas will fade against the background of Kellhus' Ordeal. Just imagine a moving topos, planned by dunyain & fueled by devoted zealots, going right into the outskirts of hell. A big torpedo for a big ship.

Erm, Gin'yursis was the king of Cil'Aujis, located to the north of the Kyranean empire.
Nil'giccas (aka Cleric) is referred to as the greatest of the Siqu by Akka.  According to all the info we have, the non-men of Ishterberinth probably conducted the tutelage among the Norasai pretty much exclusively.

Aw! Good point, but I was mostly referring to this:
Sos-Praniura was a Gnostic sorcerer, the greatest student of Gin'yursis. In 684, Sos-Praniura founded the Mangaecca, the School which would later become the Consult

But how is he still alive?

Here's a version about accidental time-travel. :3

Titirga was one of the brightest gnostics in history and needed a quick solution to his lil problem (no earth's echo to cling to — no possibility to walk in the air and save himself from falling down). Where Kellhus took cants of chatting and remade them into a teleporter, there Titirga could try to rethink the very idea of walking in the air. As they say death's proximity creates wonders.

Why use an actual and perceptible echo like some petty anagogic schoolmen? In general it's too demanding & blunt, in particular it's certainly impossible. So like a true gnostic he applies a wide abstraction of such echo, which is pure and elegant enough for sorcery to make all the work and to round all the rough edges. Poof! His wish is granted. He safely walks over the same earth again but paying the price of the different time (as a resulf of massive generality of his abstraction).

Literally Titirga is so badass he pierced the time after he slipped.