I'd say it more performs like a Bishop (3/3.5pts), but is priced like a Rook(5pts). It's not in a bad spot, and you can certainly have success with it. But it is a bit overcosted.
The compounding problem is this:
For the points you have to pay for a Defender (30-50 points), it needs to be the centerpiece of your list. It needs to be the thing that every other ship on your side is supporting, either by distracting your opponent, or adding damage to the Defender's attack. The Empire simply has better options for that.
Keeping its Centerpiece status in mind, it really shouldn't ever have an ion cannon. And its unique dial means it will have a hard time flying in formation to allow it to be supported. A good Fel or Whisper can stay out of its arcs. It ought to be a good match against a Fat Han*, especially if the Defender takes an HLC.
So that's where I see the Defender. A good ship that doesn't quite fit into a great list. A good list? Yes. But not a great list. It doesn't need a price break, or a power buff. It does need _something_ only it can do, in a way that benefits a few other ships.
That's why I like any ideas that let it add an ion/stress effect to its basic shots. We don't really have any board control centerpieces, and the Defender would make a nice one.
*I need to open a Chinese restaurant called "Fat Han's".