I totally agree, I looked at options for Mykonos and with the $50 off the tour was quite reasonable for once. You will still need to pay for chairs and an umbrella but you wouldn't have to worry about transportation and linguistic. And unfortunately for the Epic it states it is a tender port so booking through them made sense to get off the ship faster.
A local guide told be it is usually Elia or Kalafati beach. I plan on asking on Epic facebook pages where they went, but of course, the first cruise on the Epic to these ports doesn't start until this week.