I get that, but the new Frozen attraction itself will be enough of a new draw to Epcot, a meet and greet is something simple that could be offered at both parks.For just the reason you mention, though opposite.
Everyone goes to MK. They don't need A&E there to draw in anyone.
However, lots of folks skip Epcot. Put A&E there and they will go.
It has nothing to do with characters in multiple parks. They do that all the time