Personally, I think that no beginning radiant is truly "worthy" of their powers yet. When Dalinar bonded to the Stormfather, all he had was a promise that he would try to unify Roshar. Later, he was able to make good on his promise. One could argue that he was worthy at the beginning because he had changed and wouldn't repeat his past mistakes. One could also argue that he was unworthy because, as of yet, he had barely been able to unite anything. I agree with Leuthie that Navani is a unifier. I also think that she is worthy of her power. If you are arguing that Navani is not worthy yet, just remember that the First Ideal is really just a promise to try. Navani has promised that she will try to unify, and, in my opinion, she will make good on that promise.