Well, perhaps. But I suspect that overcoming one's most deeply ingrained defense mechanism is so rare as to be essentially impossible, at least not without major trauma and a complete personality overhaul. The growth/integration and stress/disintegration paths
describe what happens when you do begin "getting over it", how we naturally tend to gravitate towards a new perspective based on the previous defense mechanism. When a 6 begins learning to trust their inner selves, they naturally develop the "antidote" to their vice of fear, which is faith, the gift of the 9. So a 6 who self-actualizes to the furthest extent becomes a sort of 6-9, with the perception of the 6 and the healing power of the 9.
The same is true for all the other types. When 9 begins learning to face the world, they naturally develop the antidote to their vice of denial, which is self-assertion, the gift of the 3. They become a sort of 9-3, with the transcendence of the 9 and the initiative of the 3. Then finally the 3 who begins learning to feel their own deepest desires naturally develops the antidote to their vice of deceit, which is equality, the gift of the 6. They become a sort of 3-6 with the polish of the 3 and the humility of the 6.
I would imagine that most phobic 6s tend to be submissive, but I wouldn't go so far as to say dependent. I don't know about most 6s, but I have felt that power imbalance in relationships before, but do not in my current relationship. I think we share equal control, though we may wield it differently.
It could? I'm not sure. I feel empowered when I do things independently, but I'm also an sx/so, and I feel best when I'm around people. I don't really like doing a lot on my own, but I relate that more to my instinct variant than my enneatype. My 6w5 INTP dad is very independent, though. He's some combination of sx and sp.