I haven't played enough campaigns yet to get a good handle on how the balance of factions plays out, but I think you've definitely got a point.

Egyptian domination seems to be a well-worn theme in these forums (especially those mysteriously armoured axemen), but the predictability of the other factions is interesting. Back in MTW, there seemed to be a lot more balance between the different factions, possibly because a lot of units were broadly similar. Apart from the stay-at-home Danes, I remember campaigns where Sicilians, Turks, Italians and many others cut a huge swathe across the centre of the map.

There was a thread a week or so ago (in the colosseum? can't remember...) where someone had dissected the file controlling faction "personalities", and they had some interesting suggestions as to how to balance things out a bit more. IIRC, they were particularly keen to liven up the Carthaginians and stop them being quite so domesticated.