Merchandise sales. Now, instead of just selling T shirts to park fans, they're selling T shirts to park fans, and Marvel fans. It also did boost attendance, if only temporarily- which helps food sales in the park, as well as merchandise.
It was also intended to help hype an upcoming Marvel land, and helped give Marvel an actual presence in the parks, which should do a lot for park attendance and merchandise revenue over the next decade as more Marvel enters the parks.
It also acts to bring in out of towners, or less regular visitors, since it's something new.
I understand you have a vendetta against Mission Breakout- and I get it, I have the same vendetta against the new Fantasmic, but I'm not sure I understand the points you're trying to make about it not helping DCA- since it's my understanding that it has. If it were a garbage attraction, that'd be another story.