This would functionally replicate the situation talked about in the blog a page or so ago - forest dwellers with plenty of fruit on hand all year have no reason to organize or advance their technology.
That smacks of geographic determinism, the whole idea that jungle cultures failed because it was too hot to think. We've moved past that now. A correlation not causation issue.
The real problem with the tropics (off the top of my head) is really resource scarcity for more advanced technology. There isn't the available surface metals that there were farther north, which I think Jared diamond in guns germs and steel did cover.
Your notes about elvish modes of tree-attack indicate that you can see many avenues for the advancement of technology. Agro-tech to prune, splice, cross-breed, clone; otherwise increase yield, reduce spoilage (refrigeration, even passive evaporation based) can go hand-in-hand with militaristic applications.
If, as you posit, the fruit would cause territoriality (I think we're familiar with the elves possessiveness of the forest), the force behind military technology is certainly present.
On the subject of powerful beings:
Demons and Devils are probably safe to assume are evil powermongers. What about the other forgotten beasts that end up taking important positions in Human Civs? Are they necessarily an evil influence on the civ? Are we going to see benign Lizard monsters and the like? How do you see these creatures ultimately influencing how the human civs act?
How about
Are there non-violent/evil ways for an entity to assume/use control? I could see anything with spheres eventually having desires that are best implemented at the nation level, so I'm sure we'll get there later.