Ugggh hate those things too. :( I think I dealt with them like this?
Step 1 sab/syn/sen: have the sab debuff it while the syn buffs everyone and enthunders (I think it's weak to thunder?)
Step 2 rav/rav/sen & rav/com/sen: basically just keep the sentinel out to take the hits from all the other enemies that get summoned. bump up the % with ravagers and pull out the commando every so often to keep the % from dropping.
...then just repeat. Use a medic if need be. @
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