The stockpiles of armguards/greaves/whatever is a known bug where you can be awarded the same loot over and over and over.
Agreed on your general AI points. I don't think it thinks about defending and holding territory. More like get there first no matter what. Which, I don't consider smart.
Re: Magnar specific, It's harder than it sounds to get the shard you want / need. It should go for fire whenever possible, but have some backup plan if it winds up with earth or air say, at its starting city. Agreed on the humanoid hunting, Magnar's population will always be on par or higher that way.
Thumbs up!