There ist one thing your wrong about. The person doing the kiting and thus stacking the debuff isn't the only one taking the increased damage. The whole raid does!!! By stacking the debuff to 25+ you put unnecessary stress on your healers!
Thats exactly how this fight should be doen! Just have enough dps on the legs to be able to kill one every 30sek. After the first 4 are gone of course. The rest should go hit the boss. Killing the legs faster isn't an increase in raid dps, but a loss. Your dps end up doing a lot of target switching and moving.