I just won the Coast Range scenario on Very Hard AI Difficulty when I thought I was about to lose because towards the end Petra seems to give up for no reason. I managed to repel a big attack (losing like a third of my territory, which was almost half of all land) and from then on it was a walk in the park... not sure what's the underlying issue, but I feel I should have lost. Open maps are a bit hard to defend with such a low population cap, unlike the Isthmus of Corinth, but I guess I have to be more aggressive.
In short, it seems I just have to hold my ground until the AI has an existential crisis.
That is perfectly fine. Improved and additional floral and landscape assets would definitely be appreciated as well! Some new cliffs, mountains, trees, shrubs, rocks, anything like that.