Counselling would be under Medical. Meanwhile since Tasha, Worf and Tuvok were all simultaneously tactical/security officers, you have to wonder if they are at all separate departments?
The department heads all reporting to Tuvok makes sense to me. Even if Chakotay is more than just a 'token' gesture on Janeway's part, the truth is that he isn't Starfleet, nor is he anything more than a provisional officer rank anyway. Tuvok is the highest ranking Starfleet crewmember on board after Janeway herself.
Provisional ranks were regarded as real on Voyager. When they met up with Equinox, we should have seen Janeway make a speech to the Equinox crew about how they had to pretend like they all did that provisional rank was real rank, nudge, nudge, wink, or else the terrorist skin get uppity. B'Elanna and Chakotay would have taken those jobs if they were not real.
You forgot "morale." We all know how much Tuvok enjoyed the daily report from the ship's morale officer.
Morale I'd include in with Counselling. True it may be an off-shoot of medical, but when you look at the psychological and sociological input counsellors can have on diplomatic missions I like to make them a little department on their own. But that's just me.
Even though the Doctor started writing in Counselling upgrades to his program in later episodes? Although according to Futures End he was writing comprehensive psychological evaluations of the entire crew as early as season 3.