Using a DPS you will need to utilize healing quite effectively, and that DPS needs to bring a lot to the table to render out a Healer.

Also depending on how high you go up the ladder, the more insane it is in terms of your opposing team knowing what is coming and having a plan to counter you.
A lot of the high ranked teams after the first match up if they lose will load up a lvl 1 alt on your server or Horde/Alliance side to find out if your in the same game as them. People do everything possible to gain an edge ><
For instance I have had high rated teams completely swap out their entire roster just to try and beat me, it went from a Triple Melee DPS team to Triple SL/SL gnome Warlocks lol, it was an amazingly painful fight but still managed to win 30 minutes later on both games.