From what I gathered from the events at the lake. The Echo and the Blessing of Light are two separate things. We haven't lost the power of the echo, we have only lost the blessing of light. It seems to be a test, instead of a punishment. In addition, I get the impression that something is wrong with the power from the blessing of light, like she gave too much of herself and in some way is weakened.
It could also be that in some way, Hydaelyn has been corrupted.
Given that we are also having a land that seems to mirror some events from FFIII, remember that in that story, neither crystal is evil. When one side becomes to powerful, warriors of the other alignment come together. What if us being warriors of light is a mistake and it's Hydaelyn over reaching? We already know that there is a dark crystal, though if it has been named I am not sure.