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.
If you draw the attention of PT, and maras, you will have quite some trouble if you are DF. If you can have a buddy that will keep an eye on you, a tank, a healer or just a sentinel that will draw the attention to himself, then yes DF will pay off. Otherwise, SS or Sab is a safer bet.