cmon, how can you possibly conclude that? what settings make this so special? warlord difficulty doesnt really favor liberty, sure you have to generate more cash yourself, but favors pure tradition as CS allies are easier and expansion spots are easier to get, great plains is not very much different from pangaea, sure large map gives a bit of bonus science with more cities, but not enough that this would not be better than 4 cities, im not saying that i found the perfect combination, im saying that given the circumstances that you have lots of nice expansion spots, trad/liberty does better than trad alone.
There are several things which makes your settings favor liberty, happiness and good dirt being 2. Also don't you get policies/techs/pop quicker on warlord?
You need to play on at least prince to make the comparison reasonable (shoshone on lower difficulties also finds more ruins). Even prince is questionable as it's easier to go wide on lower difficulties because of better dirt.