absolute balance could only be achieved by each faction having the same unit selection.
i like having different factions with different selections, but it makes it difficult to say wether factions are balanced or not. even if they were balanced, having won once with each faction wouldnt be an evidence.
Aye I fully agree with you there. Having clone units for every faction would be ideal for balancing, but it's damned boring

muslim factions could use a boost
Try fighting on a desert map instead of Grassy Flatland (most used map), they get a good boost there, enough to make them more then competetive.

secondly and going along with that previous point, germany doesnt get pikes, they get 2 handers as late era units, england gets billmen, byz gets only van guard, these 2 handed units for whatever reason do not have appropriate kill rates, thus affecting balance

there is a reason those swords are so long, these things called pikes
Don't really follow you there, my bad