The aim here is for each policy tree to have some choices with universal appeal, and some specialized. Piety is the best example of this. The happiness early in the tree is useful for almost anyone, while later policies are more focused on culture victories. Based on the results of this poll, and my own experience, I think this goal is met with the early policy trees.
The harder problem is late-game trees like Autocracy, because of the way Firaxis did some early balancing efforts.
Autocracy was already rather subpar when Civ 5 released. It was rated at the bottom of favorite tree polls on the vanilla general forum. Firaxis then blocked policy saving, which was
intended to prevent an unusual exploit where players save up all their policy points until the end of the game. It was a more successful strategy than normal policy selection because of weak early trees, and cost-reducing effects in late game. This mod had already fixed those problems so the exploit wasn't an issue. The mod's approach was more complex than a policy-saving block, however, and Firaxis took the simpler approach.
However, the unfortunate side-effect of the saving block was to further reduce usefulness of late game policy trees. In the past we could save up policy points when approaching an era transition to invest in the next tier tree. With that strategy Autocracy is actually quite good. I removed the policy-saving block last summer. By that time most players were accustomed to the block, and don't strategize for policy-saving any more. This is the primary reason a tree like Autocracy is so difficult to balance now. It comes so late that if we don't save policy points, it's very hard to give it a sufficient impact on the game.
The damage from the policy-saving ban is done, and by now I think it's irreversible. I've tried rearranging policies in the trees, buffing them, making them more useful. I don't think that's worked either.
Would it make sense to try a more fundamental approach now? We could rebuild the Freedom and Autocracy trees with new primary focus. The focus could fill some sort of mid or late game need current left absent.