Also, we act like these worlds aren't connected and that
a person literally has traveled between them and gotten souvenirs to bring home. People from other worlds know each other too. Merlee comes to Flipside despite being in World 2, and we see The Overthere is in the sky on Earth clear as day. World 4 is just Outer Space, literally they refer to it as "the universe" in the flavor texts that support it. But the shopkeeper NPC is able to get up there and constantly talks about his shop being in different locations. Are we to assume all NPCs have the ability to cross dimensions which "are entire universes" without those Dimensional Doors before? Cause they only appear due to the Pure Hearts being placed in a Heart Pillar.
There's no mention of all dimensions being in danger in SPM, only a vague "The World" is ever said as well. The only explicit other dimension was the world where Mario came from which wasn't implied to be in danger at all in the Japanese version.
To assume things as grand as we currently have them due to the English version doesn't seem to be what's explicitly stated in the Japanese version and seems like a desperate excuse to keep the current ratings.