Our ferry in early June stopped at Santorini (we avoided it on purpose as we ultimately decide we have no desire to fight the hordes of daytrip Instagrammers ticking off their bucket lists). Just what we saw from the harbour - cruise ship upon cruise ship, buses lining the road up the mountain for kilometres - confirmed my worst fears. I was truly thankful that we resisted the pressure of: "But you have to go to Santorini!"
A similar thing in Mykonos where we overnighted before our flight out. Two ships in harbour including one truly gigantic monstrosity which actually ruined the view from town! So many people it was actually difficult to walk in the narrow streets. Until they all went back on board for their dinner...