never take the GW website as cannon... they make lots of mistakes and take decades to fix it!
for example, one the empire page they actually have a listed tactic for their detatchments being;
parent unit of 20 free companies + 2 free companies detachments. nice, simple... only problem is, it's actually illegal as only state troops can be parent units!!!
basically, if a unit doesn't actually 'use-up' slots on the FOC, then it cannot be counted as one of your mandetory choices. (as it technically has no proper 'slot' - it simply 'counts as'...)
so yes, you should still take a proper HQ as the champ doesn't take up any slot on the FOC.
cheers!