You should check with Disney for air options. It is a 50/50 proposition. Mostly, we have found Disney higher, or, lacking in flexibility. For example, they can do a reservation for you for next summer, but they can’t reseerve the seats until 3-4 months before the flights, as they don’t pay the airlines until that time. We are picky, preferring to fly American Airlines out of Dallas, which avoids many connections. If you are not picky about connections or seats, Disney may have some better options for you. Finally, check Norwegian or Icelandic Air for some pretty good deals to and from Europe. My experience (which includes over 100 trips to Europe) is there is never a simple answer. You have to check the various options based on what is most important to you (price vs ease and comfort of travel).
The worst is returning from a transatlantic and discovering one-way fares are about the same as round trip. We are using miles, but many guests are going with Norwegian Air as the price is really good.