The change in Norwegian Epic's itinerary had nothing to do with the upcoming passenger fee (this is not implemented yet and even if it was it would be the same for Corfu as in Argostoli or Katakolon). It was due to fuel consumption due to emissions regulations that apply in Europe that force ships to travel with lower speed so they don't pay a fine. Distance from Mykonos to Corfu is greater than Argostoli or Katakolon. Same thing happened last year.
The change in Norwegian Epic's itinerary had nothing to do with the upcoming passenger fee (this is not implemented yet and even if it was it would be the same for Corfu as in Argostoli or Katakolon). It was due to fuel consumption due to emissions regulations that apply in Europe that force ships to travel with lower speed so they don't pay a fine. Distance from Mykonos to Corfu is greater than Argostoli or Katakolon. Same thing happened last year.
Argostoli is better than Corfu, unless you are booking expensive excursions.