Future expansions.

1) The Faceless are hated by angels, and reasonable people (including Anton) no longer follow them.

Well, then Anton won't be leading them. But still, it was the people who attacked the elves in the War of the Bitter Ashes. A possible reason is the Faceless (you can think so after playing the campaign). If not, then for what other reason did the people attack the elves??

2) Railag asked the Faceless for help, but he didn't receive it, so he is not very connected to them.

I also watched the video at the end and know that he didn't receive help, specifically from the Faceless, but he learned dark magic from them, of course. I'm saying that he says he will leave a mark on this world thanks to DARK MAGIC, and not the Faceless, as warriors. Although the Faceless can become champions for the Dark Elves, since the use of champions is unlocked in the 3rd mission of the campaign. And by that time, everything may change.

In "Heroes 5" there is a single-player scenario in which we, playing as demons, defeat the Falcon dynasty. Accordingly, after the death of the Falcon clan, the Griffins took the leading position.

I know, I played it. The main character is a succubus. But it's not just that the Griffins took the lead...

The reasons for the appearance of the Academy have already been named. Until you provide solid evidence that the previous "clues" mean nothing. In the end, it's not difficult to adapt the plot.

Let's look at the development of the game Civilization 5. The release of the game was like that of Heroes: a regular version and a deluxe version with cool additions like a new nation and something else. Then DLCs with nations are released (there are many nations in the world, so there are many DLCs, and there are not so many races in Ashan, so it can be one or two DLCs). In general, DLCs are already a mod for games tied to Steam. Heroes may not be an exception. These "clues" are more suitable for the Academy in a DLC than in an expansion. And finally, we can say that all the DLCs of Civilization 5 will be in the expansion for Civ, and therefore the Academy, which was released earlier in a DLC, will also be in the expansion. This is convenient for players who have not bought the DLCs and profitable for Ubisoft because of people who bought the Academy in a DLC and then bought the Academy again in the expansion. Profit out of thin air.
In short, I am inclined to such a vision of the future:
1. Release of a DLC with the Academy
2. Release of an expansion with two types of elves and again with the Academy.
3. Release of a DLC with dwarves... or an expansion with dwarves... and that's it.