NCF – Extended list of Neutral creatures.

It's not random, because firstly, it doesn't consist of elemental schools in itself (Ashha created the elements from the primordial, and not vice versa - that is, the primordial contains the elements, but the elements do not contain the primordial). Secondly, since the elements were created by Ashha, they are primordial magic associated with order, not chaos.
Demonic creatures mostly use:
1) Primordial magic in its pure form (spatio-temporal spells, including opening portals between dimensions)
2) Chaos magic (a form of primordial magic corresponding to Urgash)
3) Elemental magic corrupted/modified by Chaos
P.S. Everything I write comes directly from the lore, not from my imagination.
P.P.S. We need to remember again that the lore of the fifth part somewhat conflicts with the lore of the 6th and 7th parts. (for example, in Heroes 5, demons prefer darkness, although the Dark Elves hardly study it:smile07: - in my opinion, complete nonsense)

Regarding the first points about primordial and elemental magic, it is written in the legend of creation: "Ashha separated and defined six 'colors' of magic floating in the cosmic void: Darkness, Light, Earth, Fire, Water, and Air." So, Ashha SEPARATED the magics from a single one (logically, this is the primordial). Again, there is a reference to the fact that Ashha is a dragon of order, she organized chaotic super-magic into constituent aspects, and another reference that a world without any magic or religion is impossible, and therefore the Voidwalkers wanted to kill the god - then the whole system would collapse, etc.
In the same legend of creation, it is said that Urgash hates all of Ashha's creations and wants to plunge the world into primordial chaos.

According to this logic, ifrits should shimmer with all the colors of the rainbow and cast primordial spells... Well, I'm getting carried away... I need to think further

Added 3 minutes ago
Regarding demonic magic, I completely agree