I am almost afraid to say this, but... this is actually a show where Decade's dimensional travel would have worked.
They have a pirate ship, and they are supposed to go out and find "treasures"
It would have made more sense for them to be sailing around in space, going from one Earth to another, meeting up with the teams from those worlds.
Having all the Sentai teams being from the same world is a bad idea, and it eliminates the chance of writing themed episodes for each past team.
I'd much rather have 35 different worlds, where the Zangyack has either destroyed the old villains or forced them to team up with them.
"But what about the legendary war?!" you say?
Well, that is pretty easy. The Sentai teams failed to save their own worlds. So they all teamed up and took off to one of the planets that Zangyack was about to invade.
I could care very little about seeing the old Sentai teams fight, as this show is about Gokaiger, not Magiranger, Dekaranger or whatever.
However, being an anniversary show, it WOULD have been fitting to see the Gokaigers fight in a Magi-themed world or a Deka-themed world, and see how each has been affected by the Zangyack invasions.
Imagine past grunts walking around with Zangyack armor etc. There is SO much they could have done to make this show more of an adventure instead of: “Let us float above the same city day after day, and wait for some guest stars to pop up”