Those are not Shamans, they're Warlocks.
Warlocks are fragile. Here's one way to deal with them:
Have your ACTUAL Shamans (single larger blimp) cast Immunity on some Hunters and have the Hunters attack the warlocks. Immunity will prevent the Hunters from being polymorphed, they're fast enough to take little damage from the meteor swarm (if you order them to keep moving. If the Warlocks cloak, Hunters can have the passive "Reveal" skill, so the Warlocks can't hide.
Your Shamans could also cast their fear spell on the Warlock groups to paralyze them.
They're also easy to kill with your Dragon.
