So I was struggling to get used to the fact that firing a magic power required (with gamepad) holding one trigger to aim and then pressing another button to fire. It feels slow and cumbersome. On mouse and keyboard you only need the right mouse click: you hold it to aim and release it to fire, which is what feels natural and what many games do.

To achieve the same behaviour on gamepad, all you need to do is to go into the control settings and map both Aim and Fire to the same button, like Right Trigger for instance. So what will happen is that while you hold the trigger you're aiming the spell, then when you release the trigger you fire the spell. Let me tell you, it makes firing spells in combat or using the grapple beam SO much quicker and more intuitive. I wish this was the default behaviour. Hope it helps someone else.