I can't speak for ravaged or swamp, but as far as the other maps go, eventually the lands heal, and the settlers cometh. It does seem that after the Blood Moon event, likely because no one currently ever signs peace treaties except with the player, the settler swarm dies down, to be replaced by troops. The AI seems to focus the resources it used to found new settlements to instead take them from others. Possibly this will change with .80.
In my current game the AI has been at war for several hundred turns, I'm not sure that they have built any pioneers during that time. There's a chunk of land available due to my clearing a couple of wildlands, right on the AI's borders, and they've ignored it. One of the AI leaders wandered the map after losing his last city, and never attempted to resettle, finally dying in battle long afterwards. My guess is when it gets down to one AI, they'll start spamming pioneers again until that free space is locked down.
As a long time Civ player, I wouldn't mind the need to spam settlers just to keep up with the AI quite as much if there were an easier means for controlling settlements. Currently, it's a bit unwieldy after you have 10 or so. The UI thread has several good suggestions regarding this issue. More slider options at set up would be ideal.
Something else I've noticed about the AI's habits concerns the settlements themselves. It's very rare for me to capture an AI settlement that contains a workshop, and I don't think I have ever captured one with a mason or higher. While my own cities have long since reached their maximum growth, the AI cities are sickly and weak by comparison, including the capitals.
All things I'm sure will be worked out in time, looking forward to trying out the new version.