Walkthroughs for custom maps.

Tell me how long it took the Chinese players to complete it.
I'm stuck on the isthmus at 19-4-7. I feel like I don't have enough troops; I can't break through Brissa (9+9 Titans, 6+6 Archons, and other minor units).
Or am I just being incredibly slow?

I don't remember how long it took them to complete it. There's a walkthrough of this map on a Chinese forum, and it describes the beginning of the game; it might have been a couple of months. After that, either the player gave up or decided not to make everyone wait for a 20-month review. :)
From what I saw in the walkthrough, they were much faster than me. But I started the map without detailed planning, so it didn't turn out very well.
As far as I remember, such huge stacks are defeated like this: clone on bears + morale on bears and their clone. Against Brissa and similar enemies, you should have something like 2-3 thousand bears, which means 4 attacks (if you have 2 morale boosts) of 2 thousand bears each, which is an 8 thousand-unit attack! It kills a lot, especially such large stacks as Titans. Also, in battles, it's better to equip everything for stats, ideally with the Alliance artifact. Cursed armor almost always prevents you from winning.

Also, as far as I remember, on the map, there's an opportunity to defeat the Azure Dragons in the north, take the Book of Air, and simply "fly over" a couple of difficult heroes. That's what I did.