Right now it seems that the only things heavy attacks are good for are:
- damage for low level characters who don't yet have enough resources/regens to spam several spells
- to replenish a few % of resources when you don't have enough for any skills
- knocking down unbalanced enemy
It's just not worth using heavy attacks unless you're a healer with resto staff. Their damage, even AFTER buffing them with things like Flawless Dawnbreaker, Surge or Molten Weapons (which takes almost 2 seconds to activate and last for only 2 pitiful heavy attacks till you have to reactivate it..), they still deal hardly equal damage over ~4 seconds (that is including animation and all) what an instant skill does over 1 second. That's 4x less dps compared to spamming instants/light attacks.
To make weapon based characters truly working, dps should be holding steady whether you spam instant abilities or slowly swing your weapon. Which means increasing damage of moves that take longer to perform and reducing damage of some more "OP" instant casts. So light attack/instant spell should deal less damage than spell with 1.1 sec activation time (+animation) and that spell would deal less damage than fully powered swing of your weapon (which takes around 3 sec just to charge up + animation).
Right now the heavy attacks are just treated as fillers for when you run out of resources.. while it would make WAY MORE SENSE turning that around - making heavy attacks the main source of damage while skills would be just fillers with additional utility, pretty much like most DK's abilities already are (DoT that punishes refreshing, CCs that make mobs immune to CCs for a while, AoE armor reduction for several seconds (but with low damage and DoT to punish repeated casts), passively increasing crit while shooting fireball once in a while on an enemy in range, ...).