This has been around for a long time, since maybe even WOM days, but the AI sovs seem to have some weird fetish for leather greaves. Not only that, but they aren't equiping their best armour. Here is Verga, he'd rather use the leather greaves than some nice chain greaves. Plus he has a helmet that is 6 defense which he doesn't seem to bother using. And a shield could help.
And shouldn't he be selling all this other stuff that he isn't using? I mean it was like a treasure chest for me to have him surrender, I ended up with much better weaponry for my heros. And with the newest update coming out where troops can collect stuff and it goes to the sov, I imagine enemy sovs will have even more goodies in subsequent releases.