This could also work, as they're both centered around you, however both Unleash and Abyssal Drain function as enmity increasing skills. Quietus is a damaging/MP-regen skill.
I think it terms of 'muscle memory' I use AD for the same reason I use Unleash, while Quietus is used for something completely different.
That said, I could probably get used to it if they did do this.