You'd rather Capcom never speak of DASH3 ever again?
Depends on the context in which Legends 3 is referenced. Aero, Barrett, Trigger's L3 armour--all that's fine. Resolving the series's cliffhanger in a short event (if that's even what the event's about) in a JP-only social crossover game...isn't.
The impression I'm getting from Capcom is that they want to deal with Legends as little as possible (see: that godawful Xover trailer from which Trigger is blatantly mostly-absent, along with any Legends logos); only Tron and her Servbots are making any real appearances, and it's probably only because she's been in crossovers before and can easily fit into them without much Legends association (to a non-fan, anyway). Thus the rocket feels a bit "there, now we don't have to talk about Legends 3 anymore because we took care of the cliffhanger in a non-canon game".
Or maybe some individual staff member didn't think things through.
I really wish they'd give Aero or Barrett or even one of the "Lily" designs a cameo (Aero did appear in a calendar, but I think its art was completed before MML3 bit it); that'd be potentially less controversial and a sign that everyone's contributions to the game weren't completely wasted.