Molten Armaments vs Igneous Weapons

Stam DK here; cp265 or so (PS4).

I run the typical meta for DK, based on HA weaving and Molten Armaments. I don't run any trials yet, as I mostly just group with a few friends for Vet dungeons and what not.
I know I can run some sessions against a training dummy and get the overall dps change, but can anyone give me any experienced comparison between running Molten Armaments over Igneous Weapons?

I get the huge 40% buff to HA is great, and we effectively do it between almost every ability... But don't all the abilities calculate a portion of their damage off weapon damage, so wouldn't Major Brutality buff everything to some extent?
I know most people get Brutality from another source, like pots, but I don't have the luxury (yet) of popping damage pots all the time, and no one in my dungeon runs provide the buff.

TL;DR - How much better is 40% buff to HA only than 20% to weapon damage, which contributes to all attacks?