20% crit, 15% crit nova, >+24 Arc on Crit, and ~7% haste can fully support its mana expenditure during multi target engagements. That is in no way expensive. You will lose out on raw dps on the weapon, offhand, and pure int on the headpiece but while you lose out on the number on your paper doll you will likely come out ahead... gold piece for gold piece.
Why the obsession with arcane orb? It has terrible return on critical ramp for both arcane as well as cooldowns. Well placed star pacts can work just fine in a kite situation.
You can even use star pact as your "signature move" to generate mana for your arcane orb use.
Single target arcane stability can be remedied by blending in a signature for a while until you're more toward 35% crit, but once again that line isn't very hard to get to.
Because you can SPAM arcane (pro tip: 20 AP vs 35 star pact), because it hits the first thing it comes into contact with, because meteor FCKING SUCKS?
arcane: 20 AP, 175% damage, EASY TO TARGET
star pact: 35 AP, 200% damage, YOU CANT HIT ANYTHING WITH IT unless you are melee wiz