We'll get to see what happens in a few days and one side or the other will get its vindication.

But realistically, the argument against this being a thief or at the very least that being a dagger is getting more and more far fetched. A Dragoon? Are you serious? It looks NOTHING like a spear, the handle is extremely apparent, and he is holding it with the blade down from his hand. Just like a bow, the body of the spear would clearly extend into visible range.

There is nothing behind him, you can see the negative space with your own eyes if you pull your head out of your rear. The only question is whether or not we will see this new class in 2.2, not whether or not it is a new class. And I would be extremely surprised if this was a tease with a significant lead time. Surprises are much more up their alley than teases with huge leads.