Apparently he's Human, and an intelligent one at that, but maybe because the game thinks of him as an Orc it restricts him to certain types of armor. I've only been able to fit him out with Dread Armor and Magic Plate. This says to me that he wears "normal" size armor (not "Large" for half-Ogres or "Small" for Gnomes and Dwarves), but it must be magical. Except that I can get him to wear Metal Boots and a Goggled Helmet.

Interesting. I'll have to deck him out in Magic Plate one of these days. Even in the end game, I only had him in Red Barbarian Armor, Dread Plate, or particular varieties related to these.
His armor selection doth be crap. Verily. I usually find him worth it once I get him in such armor as he can wear.

I think those are the only ones (I didn't know he could wear Magic Plate either - try other types of magical armor (Magic Chain, Arcane ____, etc) and see if that works, that would show that it is magic armor he needs (but I feel like he is supposed to only be able to wear the "barbarian" armors (since he is classed as an orc).

In terms of the helmets and books, can't you get everyone to wear those (even half-ogres)? I thought you could, and the only restriction for half-ogres other than body armor is on some small weapons (are too small, or something like that).

Well, yeah, he can wear any sort of hand, foot or head armor. It's just the body armor that seems to be unusually restricted. I kinda wish Troika would have thought to add a "What kind of things can you wear, X Character?" question.

The UI is by far and wide one of the worst things in Arcanum. I would've also liked some control over my companions and better combat, but man, the UI takes the cake.

I'd thought that since the game was a modified Fallout SPECIAL engine, or whatever it's called, that the player would be able to do more than tell followers how far or how close they were supposed to be to the player. And then I did some reading and found that the Arcanum engine was developed from the ground up by Troika's in-house team, and since some of the guys who work for Troika worked on Fallout, they implemented a few cosmetic similarities to the SPECIAL engine (except maybe the AP system, which works almost the same), but that was about it.

I mean, it boggles the mind to try and figure out why they didn't include "I want you to fight defensively/aggressively/I don't want you to fight at all, just hang back" follower control options.

On the plus side, they all seem to know what weapons and armor are best for them, and automatically equip them when you place the items in their inventories. An example of an exception to that is when I want Jayna Stiles to equip a bow instead of a melee weapon, I have to make sure she doesn't have any melee weapons in her inventory (I prefer her to fight ranged, since she's pretty weak; And she's a half-elf, so she ought to automatically have some affinity for bows, even though she's shown a penchant for Technology).

The answer is as sad as it is simple. Everything Troika did was rushed out the door incomplete.
It's not that they didn't want to spend all the time in the world on their projects, it's that everything they did was on somebody else's behalf, and always that somebody else wanted it done too soon. Troika's business plan seemed to be to bite off more than they could chew, hoping to get a big hit out there so they could demand more concessions from the next company for whom they'd work.
The result? Beautiful yet tragically incomplete games.