So sad you don't know about the shadow tree...
Light tree is efficient until you have enough ability points to complete your shadow tree, I would say until lvl 18, after that, shock abilities are... so weak compared to the power of a good shadow combo.
As you said, shock therapy is a great skill, but why wouldn't shadow players use it ? O.o There's no spell to waste points in before getting it xD
Insecure + Psycho form + epiphany + nightmare + shock therapy (can add terrify before epiphany if you're taking too much damages) = Kill a 15k+ hp enemy without loosing health (recovering it).
In zone 5, a nightmare used like that does 6k+ damages, 8k in zone 6...
Shadow tree rules.