I think you should check your maths, 3x5 =15, not 35

Just tried this out in a few games. I think it's a pretty solid build. Your right about the portals, i've played many games and almost nobody uses them. It is better to simply use them as an escape/engage tool. My only exception to your build would be at level 3 The Master's Touch. I prefer to use Arcane Explosion. Having to nail down 35 hits (heroes) to have an effect is somewhat annoying to me.