Power Girl's outfit is made as a parody of the entire super-heroine-revealing-costume-trope.
The problem is they decided to change hers and make all the other ones even more revealing, so they're trying to distract us from the fact that they're getting worse by fixing up the outfit of a parody.
The artist and creative team on worlds finest where not the same ones who did super-girl and the outlaws. So you can't blame them for something everyone else is doing. They were trying to be innovative but when they were swapped out the new team decided to give her back the cleavage outfit because nerds complained they couldn't see her boobs. Also catering to nerds who are in their 40's is a bad business plan. You still haven't explained why her new 52 outfit was terrible.