Lethargy is a 1pt wonder. You can allocate a point to take advantage of the +20% bonus magic damage. It’s not mentioned in the tooltip, but here : Lethargy hidden effect. Don’t forget the attributes! They’re pretty useful. It may not perhaps be the case for you depending on your build but they help party members immensely.
I’d allocate your points like this but this is personal preference. In any case, you have 9pts to spend as you wish. Neither Earthquake nor Energy Bolt [does not] scale well into late game and (assuming it has not been fixed) I believe Earthquake breaks links so that could be a problem in party play.
As a final note, you may want to post your own topic on the subject. Not sure how much traction it’ll gain but at least you can ask more specialized advice for your build.