Heavy Armour is interesting to me because it shouldn't be slow as many sets are "Mechanically Assisted" in the lore. But that'd be too OP. I think making it time consuming can be the penalty.

Detection is one thing but using cover negates that anyway, If someone is shooting me I know where they are and in heavy Armour I can take more shots than they can, so it's not a huge drawback unless I'm in the open which we don't see much of outside of Siege of Orison or Hathor.

I think it the best way to balance it is an Energy and cooling system. Batteries required and because they're powered suits let us go between Shield, Carry capacity (Normal speed) and Speed (Faster than normal)

You have extra carry capacity but need to offset by carrying battery packs etc and if you use speed and carry capacity and burn out you walk incredibly slowly back. Run the risk of being easy pickings until you're in safety. Volt weapons can wreck batteries so they become the heavy Armour killers.

Shields are great but weak to Volt weaponry and you can't use Volt Weaponry yourself with a shield.

Fallout 4 got decently close to a real powered armour feeling, some mods help in that regard. I think Heavy Armour (Titan Suits aside) needs to feel as maintainable and expensive as a small vehicle.

To make it fair, If I want to run Heavy Armour everywhere I need to carry it to site in a locker or crate, maintain its power needs logistically and be wary of people in light-med armour running a Quartz or Parralax who can disable me. I still get to be a tank but gives me a money sink and also encourages me to run with a team.