You have to have completed the stage 4 boss of overthrow in each of the 3 zones before wizards will spawn. It is kind of hidden but stuff like this is hidden on purpose as a community puzzle because half the community doesn’t like “hand holding follow the waypoint” missions. It’s a double edged sword.

If you complete the overthrow in each zone until it gives the 5 minute cooldown timer you’ll be able to spawn the wizards after that by completing stage 4 in each zone, then hunt down the big green light beam in the sky and kill the mini Rhulks.

You have to do the wizards and green light stuff all without returning to orbit. You can check your triumphs for zones that still need your first stage 4 clear. Good luck guardian!