In your opinion, which hero has the most charisma in the campaign?

2 Warrior, if it were that easy to turn a demon into a half-demon or even something completely non-demonic, then no one would pay any attention to demons, but they are actually feared. And if we are looking for logic in Agrael's transformations, then he is simply IT, disguised as a demon, and "infected with demonic magic," and he hid his ears inside hollow horns; they are somewhat unnatural (the horns), and his ears stick out at a 45-degree angle, as if pressed against the horns =).
And why he has demonic troops is completely unclear; in my opinion, his own people should have torn him to pieces, burned him, and even finished him off with a meteorite. He betrayed the main demon (Kha-Belekh) and is leading his own people to their deaths (I don't think he treated them humanely after communicating with Tieru); after the mission with the tomb, they should have understood this. Although, of course, the behavior of troops in the game is rarely explainable.

And regarding Markel: Zephyr fought him again when he was trying to find and free his father. And Markel looked quite alive and just as charismatic.

Well, this scenario takes place sometime between the end of the Necropolis campaign and the beginning of the Magic campaign.

The only bad thing is that the scriptwriters were too lazy to include her in the campaign.

A clone (well, not exactly) of Lucretia is present in the expansion; her name is Ornella =). And she has the same ability.