Drain Essence as a Main attack

[eisprinzessin]

What prevents you from using it as a main attack? You cannot assign it to LMB because:

Why is Drain Essence not left bindable but mark of torment is ?

Drain Essence can be cast without a target, meaning you’d never be able to move anywhere.

But it works fine on RMB, which I use for all my main ranged attacks.