User blog comment:IamJakuhoRaikoben/Chapter 446: The Land Abandoned By God, Review./@comment-5303512-20150727051623/@comment-24264679-20150729052618

Aquarius mode and Lucy's stardress worked using two different power sources meaning they aren't the same thing. Lucy didn't need Aquarius Key to use the water magic as Aquarius key was broken. Lucy uses her other spirits power by combining the dress with the key. They are similar but they aren't the same.