The thing I think makes her strongest is that she doesn't have wasted passives, and her tree is well constructed so that you get complementary abilities, the only locked passives are on war horn, which is a strong power that is very reliable and worth using.
The old characters have trees that are marred by inefficiency, vital passives locked behind weak powers, and many, many passives that just do not work hogging the early parts of the tree.
If the other characters had passive set ups like her they would be much stronger with the powers they have, and there is evidence the devs are working on that problem.
The Katari is the character that is most overshadowed, and I am pretty sure this has more to do with his good passive abilities being locked at the far end of both trees, and all the early ones being unhelpful, rather than his powers themselves. He just needs a bunch of his passives fixed, moved, and modified slightly.