I don't think that human/AI differences in past Civ games are much less than in Wesnoth.
To begin with, I don't think the advantages the AI gets in Wesnoth are as large as some people think. On most campaigns, the AI gets quite a lot of gold in many scenarios, but the player gets to recall higher level units from past scenarios which are typically more powerful than any of the units available to the AI. I used to play Wesnoth matches involving myself and a couple of other developers against the AI. We found any game where the AI had more than a 2:1 advantage quite difficult to win.
In Civ3 I could regularly have defensive wars with other civilizations that had an immense military advantage and defeat them. For instance, I played Always War games on Monarch difficulty against six other civilizations and won. In Civ4 it's harder, but still achievable.
What one perhaps can't do quite as well in Civ as in Wesnoth is prosecute an offensive war. In Civ you largely have to have something approaching parity to actually capture enemy cities, because cities are always strongholds. In Wesnoth you can sometimes achieve a "decapitation attack" of the enemy leader.
But this is easily solvable in Civ5 -- just make it so cities are sufficiently strong that regardless of other factors you will have to have decent strength to overcome them. I can imagine a large number of improvements -- stockades, city walls, castles, etc, that one can build to make a city more difficult and costly to attack.
-Sirp.
You are talented, to make an AI as good as Wesnoth on your spare time is quite an achievement,