Since the gamepad doesn't have one, and it seems that might be a reason why heavy attacks were changed to be the pet command, why not instead map it to a button combination, similar to dodge-roll (LT + A) instead?

This would be achieved by Holding block (LT) and Clicking Left Stick (LS(Click)) which is currently unbound to any action on a gamepad.

Edit: Then allow players to toggle between heavy attack command and the keybind via an option in gameplay settings.
(Original Title: Pet Command - Remove From Heavy Attacks | Add in Gamepad Keybind)