I feel that their to boring and their story is not as in depth as the Taurethrim.I think making them advance would solve most of the issue people have with them.And it would make more sense as they clearly have trade with the rest of the Haradrim.
Why would anyone trade with them if they weren't advanced? In fact, HOW could anyone trade with them? The set lore of trading means they must've had something WORTH trading. But in the mod ,we see nothing of value from them. They still use crude weaponry, don't have ANY ranged weapon, and have absolutely nothing of value in their current lands except underground, and in the odd bit of forest, which is quite rare.
For trade, they'd have to be reasonably close to the coastline, or situated along a main road that is used often enough. We see at least a bit of this. They also own a large amount of land as a single coordinated movement against the Taurethrim. What doesn't make sense is that, in their faction stats, they are enemies of not only the tree people, but also Gondor, Rohan, AND EVEN the Rangers of the North. Which means they can travel large distances, and are known to be a threat to the Free Peoples. Which means further, that they aren't a bunch of scattered tribes, but a power of the world, albeit a small one similar to Dunland, or even Bree, but with a LOT more land. None of which could have happened on wooden tools, no ranged weapons, and animal-skin "armor".
Lore wise they trade Mûmakil and gold with Harad.As you said they should be advanced just by their alliances and the fact that Gondor finds them a big enough threat.Yeah they should have more roads,and as I posted in my suggestion they should have a sub faction who live around the coast who trade with Umbar and Harad, since it would make sense as how they can even trade with Near Harad.
Just a little thing, for the cavalry, perhaps the Morwaith horse armor would have a lion-like mane around it, seeing as (unless I am mistaken) lions are a sacred animal to the Morwaith, and they would want to channel the energy of the Great Lion when charging into war, or smth like that? It looks cool though!