Under the old "Stun Lottery" rules, the KA was the superior attack against high DEF targets because of its volatility. To demonstrate the danger that the Stun Lottery presented, let's do a little thought experiment.
Imagine an attack power that cost 5 points per DC. When you hit with this power, you roll just one die for damage and multiplied the result by the number of DC. Now, this power has exactly the same minimum, maximum and average damage as an equivalent EB of the same active points, so this new power has to be balanced, right?
Of course not. This power would be a terrible idea. Pay no attention to the averages and look at the actual results. Your average PC has a 33 -50% chance of getting stunned with any 12 DC hit from this power. Think about what that does to the game.
The new KA rules are fine. As long as you use KAs for the type of thing it is designed for: breaking force walls, barriers (ugh), machines, constructs, vehicles, and occasionally killing things. If you're trying to stun things into unconsciousness, use something else.