I know what you mean. My buddy keeps on going on and on about how powerful Scarlet will be with having the Ion Cannon and Gunner. That he is always going to have a ship with the ion token and multiple stress tokens on it. I keep on trying to point out to him that her ability is a bit too circumstantial. With crits only being around 10% chance per die.
Your friend has a good point, in a way. Kath has a 33% chance to roll at least one critical with the ion cannon; either your opponent is hit by the ion cannon (yay!), or it dodges the critical hit and gets a stress token (yay!)
But while the card text for the ion cannon says "Then cancel all dice results", I don't think that counts as your opponent canceling the result. (It's much more reasonable to say that it's either the card itself or the attacking player canceling results on the attack dice.) So Kath's ability doesn't activate unless the opponent cancels a critical result by assigning an evade result to it. So it's unlikely that you would assign both an ion token and a stress token with the same attack; you'd have to roll at least two criticals, with at least one canceled by your opponent's roll, in order to have that outcome.
To me, that chance (almost certainly under 5%) isn't worth building around--particularly not when, unlike the Firespray's equally strong primary weapon, you can't actually deal a critical hit with an ion cannon.
Back on topic: I think Wedge is going to continue to enjoy a lot of popularity in Wave 2. He's no longer the only skill 9 pilot, but he is by far the cheaper of the two, and he's going to be prized in Rebel/Imperial matches for his ability to pick off TIE Interceptors, and even more prized in Rebel mirror matches as a YT-1300 killer.
And as hothie noted, the Wave 2 upgrades make him even better than he was before: Push The Limit + R2 Astromech is an incredibly potent combo, Expose all by itself makes him even more dangerous than before, and Elusiveness + R2 Astromech is a nice way to mitigate his major drawback (particularly in combination with a Shield Upgrade, if you can afford it).
I'm on the fence about Stealth on a typical X-wing, because it's a relatively expensive upgrade that's fairly easy to take out of play--but I'm curious about it, especially for Luke. (Luke + Elusiveness + Stealth… heh, heh.)