Mace has the best base damage output of any character in the game, barring Palpatine. The only character who comes close is General Grevious, only Mace has high enough health to be relevant and exists in a color which can take advantage of his damage type (especially with Guard and Destiny). His ability may seem redundant with all that damage, but what it really does is forces your opponent to control both of his dice, no matter what they show, every time they have a character down to 1 or 2 health. That type of ability doesn't need to ever actually fire to alter the game.
As for his cost, Mace has some pretty decent pairing options, even without knowing what's in the upcoming set. Padawan keeps you mono-color, but also brings three damage sides, a focus and the ability to play a saber turn 1 (or Vibroknife for 1, leaving the other for an unblockable 4 melee from Mace). For yellow Maz is the obvious choice, bringing focus sides to ensure you hit those big 4s when you need them. If you want red (maybe there's some awesome card in EaW for it?), or just some protection for Mace, Rebel Trooper can protect him with Guardian.
I do agree that Mace probably won't be tier 1. But not every character can, or should be tier 1. Mace looks fun, and while that may not be enough to put him at top tables, it is enough to justify his existence in the game.
On a more practical note, at this point a change would need to come in the form of an erratum, and I think those should be reserved for broken combos.