The biggest problem is that the AI civs are using Warriors as city defense WAY too late in the game. It is very common for me to have taken out >6 cities with a couple of non-rushed Axemen because the AI has nothing but Warriors defending. The fix I propose is to make Archer's much easier to get. I would replace Militia with Archery. Once the AI gets Archers they become far harder to take. They can also defend themselves much better against Barbs. As it is, I almost never have Archers until I have Axemen and a religion special, and that doesn't make a lot of sense. I'd take the old Archery tech slot and add in Blacksmithing. A dead end that allows construction of Barracks (now called Blacksmiths) and its units. That way you can get Bronze Working to find copper and cut down forests, but not also give the military advantage without having gotten Warfare. And if you don't have Copper you don't have to get the tech.
Second, copper is too important in the early game. With copper you can get Form of the Titan and Axemen really early. Without it the best early unit you can get is the Drown (see below). To simplify, I've never had anything but a trivial win if I have copper start near me, and my only real loss came when I didn't have it. The fix above would help, but I'd also change Form of the Titan to require Marble/Stone regardless.
Third, the Drown are too good and too quick. The cost increase will help, but I think you also need to make OO require a different tech. It takes 3 techs to get OO, and 6 (with 1 potentially free from Philosophy) for the other two. I think you've talked about adding Philosophy as a requirement, and that would be fine, or something else like Cartography and Optics. With that and the Drown cost increase I think it is balanced.
Fourth, in the mid-game Conjurers are way too effective, much more so than mages. Even the already announced balance changes won't be enough I feel. As long as they are stacked with a couple decent defending units they aren't going to be attacked directly, the elementals are still just attackers that never have to heal. Until the Phase 2 changes I'd recommend dropping both the elemental strength and conjurer strength by an additional 1 beyond the proposed change. Or, another option would be to add a couple extra techs pre-conjurer. Sorcery would be obvious, but again, I'd just skip mages until Conjurers. Something like Unquestioning Obedience instead of Polytheism would make it a tougher choice.