I use Drain Essence as a stun in PVP. More often than not, I block-cancel it as soon as the stun kicks in. This is the only option I have as a lightning staff user. This is because Destructive Clench was changed and now only stuns with an inferno staff equipped.
The version of the ability in PTS today is really bad. You'll never get to the end of the channel, and are just begging to be bash-interrupted in PVP. Also, there won't be any options for a fast-activating stun for classes like necromancer, which will severely limit the types of build you can put together.
I would like to propose making the stun apply as soon as the effect ends -- whether it reaches its last tick, or is block-cancelled by the caster. With that, users can choose to forego the damage and get the stun sooner, or wait until the channel ends and maximize the damage. Either that, or can we have one of its morphs stun immediately but do significantly less damage (e.g. less 50%)?