That's actually the best way to explain it to DF DDs. They usually don't have the DPS to go over 4 stacks anyway so I just tell them to forget everything about keeping track of Rancor and just kill the adds as soon as possible. The kiting strategy is pretty much a crutch for unskilled, not under geared, DPS who leveled to 50 without learning their class properly.
It may sound rude and judgmental, but I always gave a fair warning to new 50s queued in WP DF that the last two bosses will be demanding a bit from the DPS and they have plenty of time from the first trash to the flan boss to improve their rotation/priority if they are shaky on it.
