I also find it hard to believe that the Overlord surrendered, but his line at the end of mission 6 of Campaign 6, "You have won the battle, but you will lose the war," doesn't sound like suffering from defeat.

Well, he had a reason for optimism (the appearance of the Dark Messiah), but whether he won this "war" is still unknown.

He figured it out. Campaign 2, mission 1, the Overlord accuses Agrael of infidelity and orders Erazeal to kill him.

But not immediately, but only when Agrael's betrayal became obvious, and before that, Agrael was the Overlord's right hand and most trusted agent, and he suspected nothing criminal.

Gotai did the same thing as Arantir: he united the disparate orc tribes.

Really? Did Gotai unite them? It was Kujin who did that, and in addition, she made Gotai a khan, and she also commanded the troops in the finale. So Gotai is definitely out.

he traveled with an army through the Griffin Empire, which speaks to his talent as a commander.

But who didn't travel through the Empire in those troubled times?
Except for Faidaen:D

Frida is Godric's daughter, who was Isabelle's bodyguard.

Well, Godric is at least a national hero in the Empire. And Frida was very popular with the troops.

Added 48 minutes ago

It has already been written above that Agrael was figured out.

I repeat once again that it was impossible not to figure him out after his obvious betrayal. So there was no need for special insight here. It was necessary to expose Agrael/Rai-Lag before making him his right hand.

On the contrary, Sareth yielded.

There is nothing like that in the single-player scenario or in the game.

And the prophecy says: "And the horned lords will bow before him who is not yet born of the lord of darkness."

The key word here is bow. I know another text: "And the demon lords will bow their heads before him who is born." These are, of course, the costs of translation, but the fact that they bow is present in all texts.

All demons recognized the supremacy of Kha-Beleth and did not doubt their Overlord.

But wasn't Xana constantly whispering to Sareth about overthrowing the Overlord and ruling with Shio and Ashan?
And after the Overlord's defeat, the demons could well have thought about seizing power. After all, some humans defeated Kha-Beleth, so why are we worse?

And he can boast. At least that the Griffin Empire ceased to exist, the Griffin dynasty perished, and the new Unicorn Empire lies in ruins. And also Irollan, the Silver Cities, Igg-Shail, and Grimheim were devastated. By the way, all these countries were beheaded. The results are not bad.

To this, one must add the defeat of elite demonic armies first in the war with Isabelle, then in his own lair, and during the siege of the Claw. Demonic sects in all countries were eliminated, and in all countries, young, energetic rulers took power, who organized an absolute alliance against the demons. Indeed, the results are not bad):rolleyes:

As far as I know, the Overlord always kept legions with him.

Legions - yes. But not the entire army. This is simply impossible.

The Overlord is the most powerful demon, and believe me, he can control the summoning of his own troops in minutes, especially on his territory, in his native element.

The most powerful, but not all-powerful. Besides, he took part directly in the battle and could not concentrate on summoning troops.

Markel united Erathia.

Markel united only the part of Erathia bordering the Empire under his rule, and the necromancers of Mythgard, and he was never the Lord of Erathia.

I don't think the spell was difficult.

If so, then why didn't the last knight of the Order of the Dragon and the head of Igg-Shail, Rialag, dispel it, who undoubtedly knew about it from Isabelle?

And the Dark Messiah was a human at that time.

Having 20 years of training with a powerful sorcerer, a decent assistant, combat experience, and a one-on-one fight behind him, and he also had the Skull of Shadows in his hands. So he was a serious opponent.