RMP's burst is faster than two healers can react to early - pre-shield the Warrior and dispel the poison/damage sources following Kidney Shot as fast as possible.
Fear and roots try to isolate your healers - keep the Warrior peeling with Piercing Howl and stay grouped so HoTs and shields overlap.
Two double-healer Warrior teams grinding it out - whoever lands a stun during the enemy's dispel/heal rotation gap usually pulls ahead.
Mirror-ish Warrior matchup - out-heal them with the second healer's dispel/HoT uptime and win the extended trade.