Well he mentioned this build cant beat him on ultimate, so I am guessing he is fighting him on elite/normal?
Well, actually you can do it. I fought against red Ravager on Elite and was capable to reduce his HP by 50% and to keep alive for some time after that.
If you have more questions we could discuss it in PM.
Updated the guide - added aether triple AoE combo build. See second post for details. 
Updated the guide - added 2h chaos cadence battle mage build. We need more chaos while waiting for FG. 