I wasn't sure this was a bug or not, so I posted it here, but anyhow, I'm about 300 turns into a VH/VH Isengard game with no sub-mods, actually beat the game about 100 turns ago; and I noticed something weird; namely, I've been at war with Harad (who's my only serious rival on the map) for about twenty turns, most of the fighting is going on in Eastern Gondor, around Lebennin and Lossarnach. Harad is regularly able to send full stacks at me (and usually keeps around 4-5 in the field near me at any given time), but the full stacks are almost always mostly Dismounted Serpent Guard, Troll-Men of Harad, and Muhad Tribesmen, with some Southron Warband, Southron Archers, and a little assorted cavalry mixed in. I only just realized, in fact, that up until this point, I'd never seen a single Mumakil unit in the fullstacks I'm facing.
Is this the AI "working as intended"? I did have the feeling that this might be the optimal army for Harad to build; my armies are basically Uruk-hai Pikemen/Infantry/Crossbowmen spam (usually in a 2:2:3 ratio of those), with lesser infantry and Uruk-hai archers recruited to fill out the ranks. Up until a few turns ago, I hadn't gotten into the habit of building warg riders, which I feel may have reduced my effectiveness, but as I was building up my newest stacks, I started introducing them in greater quantities, usually by reducing the quantity of lesser infantry and archers. I ask, because initially, the Haradrim armies were almost all Serpent Guard and Troll-Men, but the newest stacks they're deploying are featuring much higher ratios of Muhad Tribesmen and Southron Archers, which I guess would be the AI adjusting to counter the stacks I'm building (especially the Muhad Tribesmen, which were proving to be the bane of my existence, until I started deploying warg riders). But no Mumakil, even though Harad still controls all her starting provinces, which I'm certain are completely built up, and would probably be also effective in fighting me.