Well the idea of everything being some interpretation of the "real events" holds true once you consider there's at least three versions of the original Macross story (TV show, DYRL, and now Macross the First) and two equally viable versions of Macross Plus. As far as DYRL's position of popularity in the franchise, it was a pretty successful anime movie. Also, it was released on VHS at the beginning of the home video market. As such it was the first time anyone could really own a complete Macross story and watch it again and again. It's the same reason why the original Transformers: The Movie is regarded by many as an important part of that franchise. It was readily available at a time when trying to collect an entire series on tape was difficult.