My 2 cents is that headquarters units should be weak, and that you shouldn't be a slave to TOEs when creating them. I use HQs to simulate the command element, but also the logistics units within a formation. So for a division there might be a battalion or two (27-50+) supply squads, with a few LMGs and SRAAWs, along with some command squads. I have found out the hard way not to put in all of the trucks, otherwise you end up with super mobile headquarters/logistics units which is not quite right.
This means that the HQ can simulate the command and logistics support for the formation, but is vulnerable if an enemy combat unit ever reaches it. They can often fight off light infantry/SF battalions, but will normally get smashed by tank or heavy infantry brigades/regiments (as they should). While I try to be as accurate as possible with the combat units' TOE, headquarters should be created to mimic their functions, rather than the exact TOE.
I used the same reasoning in my custom scenarios. I see HQ as precious units that dictates the logistic of their units, and must be protected at all cost. An HQ that can be used to stop dead an enemy attack doesn't feel right.