How are cnidarians more advanced then jellyfish?

Sponges are less complex because they are just made of individual cells. There is no level of organization past cells in sponges. Cnidarians, on the other hand, have tissues, a higher level of organization. Tissues allow for some forms, like box jelly fish, to have eyes (this is just one of many advantages of tissues). Cnidarians' level of organization stops there though, they have no organs (heart, brain, etc.).