Don't think it'll work the way you want. It's most likely been done before, but probably no different at all if you replace the drg/mage with a RDM. If your melee are going to tank, they will most likely be /nin or Sam(/sam). If they get knocked down to 50% HP, then they probably aren't going to get Utsusemi up or a Third Eye if timers are down, and there are plenty of deadly TP moves that WILL 1 shot them. Even Colibri have one.
It's more of a risky setup for a small increase in xp/time, but when people die, then you start falling far behind.
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