Eh.. For frontline troopers (like plate is intended to be, being a tank), I value belt slots a lot more. My frontline soldiers usually juggle two weapons and throwables or utility items. This means freeing a hand and the ideal place to do that is on the belt or quickdraw. I don't juggle with stuff in the backpack as the TU cost is far too high for that. You can fit all kinds of swords (except Fuso) and maces in a 1x3 slot, which is plenty to use with the shield (since you don't have to carry a stun weapon).
I could see a buff to the backpack for the non-shielded armor (so you can carry a bardiche/fuso sword/spear: since you aren't using a shield, might as well use a 2h weapon), but with the shield, you should be using a 1h weapon and for that, the 1x3 weapons are fine. Doing this, I'd say you don't need to nerf the belt either. You either have "utility plate" or "tanky plate".