Full SS or full Sab is the only viable way to play pvp. Everything else is a joke.
I would agree with this for top level play i.e. Ranked. Long burst set-up, and dots interrupting CC are two massive deal breakers.
For normal Warzones though you can play DF and DF/SAB hybrid and have a lot of fun. With skillful energy management you can put up some nice damage totals and enjoy setting people up for huge burst kills.
I would like to note that DF isn't super amazing at killing tanks. Try killing a Jugg/ Guard 1v1 spec'd properly. They don't drop very quick. I would go as far as to say DF doesn't 'feel' as effective as it used to be a few patches a go.. but i have no explanation for that so it could just be me.