Does the updated Dark Harvest seem like a very weak keystone to anyone?

"Damaging a Champion below 50% health deals adaptive damage and harvests their soul, permanently increasing Dark Harvest's damage by 10. Dark Harvest damage: 30-60 (based on level) (+10 damage per soul) (+0.25 bonus AD) (+.15 AP) Cooldown: 45s (reset on takedown)"

Why would you ever consider taking this keystone over electrocute? Maybe if you can't get off 3 unique abilities in the span of 2 seconds, but only adding 10 damage per dark harvest proc doesn't really reward you for activating it, especially considering you need to get them below 50% to use it anyway.

It looks like it will be redundant and just plain weaker.

EDIT: On a side note, I just looked at the Overgrowth rune change on PBE and as a main I am one sad panda. That is a sizable health scaling nerf.