Don't worry about your AOE threat
I agree with everything Regill says except you want to make sure you're putting vigilance on the person with the highest threat. That is not necessarily the person with the highest dps. Make sure you're periodically checking your Omen addon to see who's closest in threat. Don't be afraid to switch your vigilance target for different encounters.
Warriors can have great single target threat but it's very difficult to tank more than a few mobs at once. There are a lot of things warriors are very good at but you have to realize you can't be the best at everything, and aoe threat isn't one of them. Consider tanking the gaunlet instead of the arena on the Thorim encounter. Perhaps a DK or Pallie tank would be better suited for the arena.
Based on your armory profile and gear, what you want to do is create a few gear "sets" for different encounters. For example I have a threat set for fights like Malygos, Hodir, and Vezax. You stack expertise and hit for fights like this. Consider having an EH set for progression bosses where dps isn't riding you the whole time. Stacking stamina in these encounters enables you to take more damage before the heal lands on you.
The way I look at prioritizing stats is by first increasing my HP, but not at the expense of threat. Only by doing bosses more than once will you get a feel for whether you need to be focused on raw HP, threat, or some combination of both. Hope this helps.