My heart has been searched. It found truth. 
1) You're correct - the microclimate of the Arbor Wilds is incredibly curious. It shouldn't exist where it does and yet, it does. The same goes for the Emerald Graves. The same areas of the Hinterlands that are that far south are covered in snow and yet.. The Emerald Graves appear to be a constantly verdant landscape. Perhaps some magic from the ancient days of Arlathan lingers there, maintaining the climate?
2) Ugh. City states. Caddius. How I love thee. This fascinates me - Sylaise's Song I feel was the greatest clue at the rivalry between the gods. Now, if each of the gods had city states dedicated towards them, that makes the rivalry all the more fascinating. It also validates the reasons for the other gods turning on Falon'Din because he began to encroach on other's lands (apparently the seas of blood from ritualistic sacrifice wasn't enough).
Taking the terraforming elf thought further...
Imshael makes offhand mention of 'the bits out west' of Elvhen territory. Orlais is full of too many elf ruins for it to have been 'the bits'. But everything west of the Hunterhorn mountains seems to be desolate. Why is that? Forgotten Ones, Blight, volcanic eruptions, the ground-shakes that Elgar'nan's codex mentions, a certain WMD employed by Andruil that turned everything into a sea of ash...
Of course, the Tirashan as a Forgotten One red lyrium cultist hub is still my favorite DLC idea ever. 
Naturally thanks to the City-State connection I pictured the ancient elves fighting as hoplites, complete with Young Solas as an Elf! Alcibiades with ridiculously buff calves. I imagine their actual warfare would consist of masses of slave-soldiers directed as cannon fodder while the high-powered priests duked it out.
Also, it's curious that the Codex entries mention how many elf ruins are in Orlais, and that the Nexus Golem said 'The Stone lives beneath Orlais', and that Kal'Sharok is (sometimes, depending on how things are with Nevarra) close to de jure Orlesian Empire. Where's Madrar when you need her?
Also, did I see Oxie like a comment? We need chemistry puns about glitter. 
EDIT: Going what Surprised Dorian/Meer said above, the Elvhen did seem to have crazy defense powers. The Temple defenses, as well as the GIANT LASE in the Exalted Plains. Heirs to the Sun's power, indeed.