What evidence supports the fact that allies in the Delian League were not equal in spite of their being independent?

Answer 1

The annual naval expedition collecting the city contributions for the League saw reluctant cities punished and looted. They did not have the option of opting out, and later Pericles admitted that Athens had turned the Delian League into an empire.

An example is the honour roll of one of the demes of Athens in the 460s BCE which shows an extensive casualty list in a year when there was no recorded contact with the Persians - these soldiers were lost in the expedition collecting the taxes from Greek cities. Other cities were defeated entirely - the citizens of Samos, initially a close supporter of Athens, were branded with an S burnt into their foreheads for rebelling, as an example to the others. Athens had turned the Delian League, formed to resist the Persian Empire, into an empire of its own, and lived high on the proceeds.