I'm finally free from work so I can give some time for a better response. Sorry for the messiness in my points below.
I'm not a fan of the greater greater demon dragons, or what have you. I feel like they detract from the overall narrative of what inferis are supposed to be. Zentherak are the apex of all demonkind, nigh-deific entities with vast size and power while endless hordes writhe beneath them. I had some reservations even in current lore that because they're the tool to attain Zar'akal, people have sometimes not treated them with the reverence and fear they deserve IRP. If your demon-dragons are any more powerful than them, they're essentially aengudaemonic tier. I don't think that's a very good thing to have, but let's go further about this. Not only are they more powerful to the extent of a deity, but they subjugate the apex demons, and they have no work to get there by default of being draconic (Zentherak take centuries of soul gathering to acquire their power). I see this as detracting from the significance of Zentherak in favor of giving it to what is essentially drakaars version 2, now with more power. The narrative of inferis is about a chaotic climb for power, where even an imp with enough time and souls could become a mighty Zentherak. By subverting that in favor of what this is, I feel as though the original spirit of demon lore is being ignored. If I were to make a suggestion, I'd say to at least make the draconic demons on par with Zentherak and only subjugate lesser Zar'kiel. Hell, moreso just make them Zentherak themselves. Ideally, I'd say scrap the dragons and make this a set of boons bestowed by currently existing Zentherak. Mixing the themes of demons and dragons only hurts the overall narrative in terms of inferis. As I said, I'm not a fan of the dragon demons. At best, I'd think a dragon would start at Zar'kiel but by no means should surpass the true Zentherak. Maybe become Zentherak themselves, but certainly not what you have here.
I see that you decided to keep the chaotic tongue unlisted from the lore. Why did you do this? Is there any legitimate reason to keep it secret? I don't think there is.
I saw somewhere in the lore that something requires an extra magic slot to perform beyond the initial one used in Naztherak. As Zar'kiel players only have access to one magic slot, this would bar them from being able to use this. Was this intentional? If so, why?
I haven't read the rest of the lore because these first glaring issues took up so much of my attention (mostly the first one). I'd appreciate if you got around to them, otherwise I can't say I support this lore.