Unless you are doing some extreme content, debuffs are practically useless. Even on most TF's the AV dies in less seconds than I can count with two hands. I am with the OP, debuffs in today's game take way too long to apply, mobs/bosses/AVs die far too quickly. It is what it is though, it's the game the people wanted, so it's the game the people got.
Prior to all the countless complaints of how hard the game was, debuffs were actually in a very good place. Power creep/"make the game easier" kind of threw dirt on debuffs in this game IMO.
Now, before anyone quotes me with a snarky comment, keep in mind, it's just my unpopular and almost never shared point of view...which has not once made a single damn difference in this game.