The strongest hero.

He hasn't lost a single battle – that says a lot.

He couldn't stop either Markel, Arantir, or Gothia while they were roaming his lands.

Only attacks and defenses? No magic or knowledge? The Overlord and Biaara are completely equal in this regard (from the last mission of the original game), and in general, it depends on how you develop them. For example, Faidaen visited so many upgrade locations and explored so many maps that in the final battle with Kha-Beleth, his defense was around 70, and the other parameters were accordingly high.

The Overlord has more parameters than Biaara.
Faidaen has 70? That's impossible. There aren't that many upgrades in the entire game. I also visit all the upgrade locations and explore all the maps, and I only get a maximum of 30-35.
Magic and Knowledge do not affect the army.

Oh, since we're talking about initiative, Railag is in a league of his own here; his "Master of Initiative" ability is clearly the most powerful, and "Terrifying" is no worse than the Overlord's "Aura of Speed."

Railag's ability is balanced by the Overlord's ability. Railag reduces it by 1%, the Overlord increases it by the same amount.

Hmm, Godric has decent defense and influences troops with improved prayer and magic; you could say the same about any warrior hero. And why Gothia, and not Kujin?

Gothia's attack can reach 80, and his defense can reach 50 if you explore everything and check everywhere. Kujin won't even reach 40. Godric also influences troops well, but he can't have such high parameters.

His spells were dispelled by Tieru and Arantir. If we're talking about who is skilled in what, then: Arantir - Summoning and Darkness (of course, the best ones), Zehir - Summoning, etc., and any reasonably trained mage of the League can teleport his form. So, the Overlord's indicators in terms of magic are quite average, if not less.

Tieru is also a good mage, especially since she is skilled in Light, which the Overlord cannot do. Tieru herself said: "a half-demon will come who will master all the magic of Urgash" - and Agrail was immediately frightened. The Overlord is even more skilled in it.
And Arantir, Zehir - they are specialists in their fields. Each has their own abilities, each has their own needs. The Overlord doesn't need Summoning, Light, or Darkness (in particular), and Arantir and Zehir are not masters of Chaos.
Only powerful, ancient mages could teleport their form. There are only two of them - the Overlord and Tieru. And no mage of the League has been seen doing this.
Tieru is gifted with special dragon magic to counter demons; it is not a fact that Arantir dispelled the spell cast by the Overlord; it could have been Biaara, or someone else entirely.

Yes, Zehir, for example. In the final of the original game, he says that their magic is far superior to the Overlord's, the followers of Sar-Elam.

He said: "Sar-Ilam was a much stronger mage than Kha-Beleth." And Sar-Ilam is a dragon. So, let's not go back to them. We were just talking about teleporting to the Silver Cities.

Well, if the ruler of Igg-Shail (i.e., one of the strongest mages of Ashan by default) is unnecessary here, then only Sar-Elam can be put here.

Who is Railag compared to Markel and the Overlord? Zero, that's who.
Being the ruler of Igg-Shail doesn't mean you're a great mage. Ilaya was also a ruler of the dark elves. Cyrus ruled all the Silver Cities. However, this does not mean that they are powerful mages. Markel was able to subjugate two kingdoms and raise legions of the undead. Mentioning the Overlord is superfluous.

Why is that? Without the Overlord, the demons will fall into despair or refuse to recognize Sareth as the new Overlord? Perhaps it won't be legions of demons that devastate Ashan, but only Sareth and the Overlord? So, let's be consistent, and if we write the Overlord among the "fate-weavers of Ashan," then we should include the other at least 7 rulers, or only Sareth and, in a more distant and global perspective, Ash and his companions.

No, but it is said that Sareth will release his father, and the world will collapse. This means that the Overlord will be involved.
The other rulers are irrelevant here; no matter what they do, they will not be able to stop/destroy Ashan. Only the Overlord with the help of Sareth.
Let's forget about the dragons.

After the final video of the Lords of the Horde. Ultimately, yes, Ilaya, but Railag started it and showed that it is quite possible (by the way, Railag is the second after Tuidhana, the only leader of the dark elves, which speaks to his strength)

I'll write about everything else later.