Well, It's always sort of been a thing with these Kaiju movies, Godzilla specifically. Toho films have more or less, been a "shared universe" for a while. Baragon, Mothra, Varan etc... all had their own movies before they joined Godzilla in a film. Even Gorosaurus fought King Kong before he jumped into Destroy All Monsters. So it's not without precedence. Yes Marvel made it a little more relevant these days, and I'm sure Legendary made the decision based heavily on how successful marvel has been...but eh...If it works it works, ya know? Besides...the more monster punching monster action the better
