That depends on your exact definition of Space Opera. At a basic level, any drama set mostly in space is a Space Opera. Everything else is a subgenre off of that.
True, the setting is mostly space but that alone doesn't qualify it as "Space Opera."
By definition, traditional Space Opera is an overly romanticized version of space travel with larger-than-life themes, melodrama, fantastic aliens and planets, vast empires, intergalactic war, and a grand scale.
Of course, we could say Defying Gravity is New Space Opera as defined by the works of Iain M. Banks, Alastair Reynolds, and Stephan Baxter since it is focused on character development and verisimilitude. However, the scale is not grand enough from the pilot script, which reads very much, as the producers themselves have labeled it, a contemporary drama set within the confines of our solar system. I suppose that's where the melodrama could come in.
You say that everything is a subgenre of Space Opera. Rather it is the opposite. Space Opera is considered a subgenre of speculative/science fiction.
Clearly Space Opera is a subgenre of Science Fiction. What I meant was Space Opera includes multiple subsubgenres under it. "New Space Opera", "Planetary Exploration", "Military SciFi", etc...
Then you were not clear in your original statement and it was far too general in its definition of the subgenre.