You can use heavy attack with this build however it's not necessary. Corrisive/Heat combination to melt Armour and score Orange criticals. You can flex out Volcanic Edge for individual enemy type mods (Corpus, Grineer, ect).

Immortal Pixie found here: https://overframe.gg/build/152320/
Dhoom Pixie found here: https://overframe.gg/build/186109/

-Dodo

Edit update:

With the changes to Berserker I have found [Quickening] is a far more viable option for speed. You can still maintain heavy attacks if you wish however I find the animation to achieve that is slower than simply straight attacking for the same damage.