I believe they are using ambuscade as a testing ground because its what is closest to a "control" that they have. Other content varies way too much from mob to mob to properly test anything. Ambuscade is the same for an entire month. By using ambuscade as a testing ground, they get content that nearly everyone does, with many different setups, using almost every job. It would be hard to test in Escha NMs because they differ so greatly and, lets face it, people are very reluctant to use DDs there until this is fixed.