I thought I remember them saying in DOS we had a maximum group size of 4 including henchmen and summons? Anyone remember this from the videos? As to the rest I agree with most of it but IMO the more ppl/mobs you need to wait on turns for makes the combat LESS fun... it makes every fight painful to sit through when you have so many actions to manage, for "trash mobs" anyways.
there are 2 heroes, 2 heroes can both have a henchman, thus having 4 people.. aside from that the heroes can both use a summon spell to get a summon.. thus allowing for maximal 6 allies while in battle. But ofcourse you can keep it as low as you want.
However in my opinion the turnbased way of D:OS is very little waiting and alot of action.
It does not feel like you are waiting for something to happen.. more like a smooth battle. And still.. the more people you have, the more things you will need to control yourself to :P