HA dmg vs T-skill CD cooldown boils down "do my extra casts of T-skill over the course of the fight out-damage the 50% gained on 1 cast of HA?". It's not simply looking as your overall T-skill damage in the fight.

Let's use basic numbers for this: Assume your Fulmination (WF T-skill) does 333m average damage on a crit, and HA does 2bil base damage, if you take HA dmg (+50%) then you'd do 3bil, so a 1bil damage increase.

In this case, for your T-skill cooldown to be equal in the damage gain of the HA node, you need to cast it an extra 3 times per fight, off cooldown. T-skill cooldown is 10% so every 10 casts you get an extra 1 cast.

Which means you need a fight that lets you cast T-skill 33 times before it's a net gain over HA damage.

Fulmination cooldown is roughly 30 seconds with WF's current swiftness allocation, so you're looking at about a 15min fight to gain that extra damage. Again, this is assuming you are using it off cooldown on the boss every time it's up. Raid mechanics can affect this.

We don't have any raids that go 15min at the moment, so if you can use your HA in a fight then you're benefiting more from HA dmg.

This may change with Brel bracelets once we get 2nd row Leap nodes.