I don't have any issues with that. People who have issues with that it's because they see it from a sexual point of view when it's totally the opposite: We come in this world naked and our natural form is with no clothes on so... it's the point they meant to use: Usagi is alone, with no weapons ( Galaxia destroyed both the wand and the sword ), no material stuff over her. Her most pure form and her only way left to fight.
Also: she was naked before several years ago in the same show. In the 2nd R opening you can see her totally naked ( with boobs + ass ), same with the S one, the SuperS opening, etc... How was people surprised to see her naked in the ep 200? xD