How Is Event Horizon Good

It just gives health and a lot of negative elemental defenses. I'm pretty sure Phoenix Wing can do better.

 

a few things really
1. the elemental defenses look severe until you realize that it doesn't affect things too much, unless you have really bad (talking -400 to -500) elemental defenses.

2. event horizon has VERY HIGH damage for a nonmythic wand. You can see this when you compare base dps (base damage times the hits per second from the attack speed). The base dps of some wands when powdered are:
Event Horizon - 753.3 [T6-T6]
Cascade - 754.85 [T6-F6-F6]
Peaceful Rest - 634.25 [F6-F6-F6]
Morrowind - 578.75 [A6-A6-A6]
Nepta Floodbringer - 576.2 [W6-W6]
Phoenix Wing - 512.5 [F6-F6-F6]
(note that powdering may vary by a little depending on the build, but this gives you a general sense)
as you can see, phoenix wing is very far behind from event horizon, with almost a 240.8 base dps difference when powdered.

3. the amount of health on event horizon is very impressive, especially for an ET wand. In fact, it has the highest health bonus of any wand in the game, and the second highest health bonus of any WEAPON in the game (beaten by Guardian, obviously).