gust+iron mist

Gust (elite lightning spell)
Target foe is struck for 10...54 cold damage. If that foe is under an Earth or Water Magic Hex, that foe is knocked down for 3 seconds.

Iron Mist (earth hex spell)
For 5...15 seconds, target foe moves 90% slower. That foe gains immunity to damage from all sources except lightning.

I don't know any other hex spell on the earth line and if so this makes the gust totally unuseful for using in an earth-lightning combo.
Would someone who has already capped gust try this out for me please?

Tbh, the damage plays a lesser role to the knockdown.
If you really want both the damage and the knockdown, use Grasping Earth or one of the many Water hexes.