Are you having more trouble with the waves or the boss?

Artak / Kimi / Scyl / Ronda / Kael or Frozen Banshee should be a team that is able to get it done.

Waves are more trouble

should just be a matter of keeping artak alive to clear waves and kael/banshee alive to kill dragon. shortonskillz suggestion seems like it would work, perhaps swapping kimi for additional reviver/healer like gorgorab if ur really struggling.

or you could try a 2nd hp burner to help setup artaks a2s to make wave clearing faster since you said thats the issue, such as morde