@King:
The problem is that you're attributing arbitrary definitions about what counts as part of a saga or not.
This is not exact science. It's giving the story a logic structure, and it's not an official definition.
The same way the WG is a force in the background of Alabasta, Water 7 and Marineford, the Yonko are background forces in Fishman Island and Dressrosa.
Being in the background is not enough. Dressrosa is part of the Yonko Saga first because it's a mid act in the overall Yonko story. It's directly triggered by the events of Punk Hazard, which in turn were triggered by the Luffy-Law alliance that was formed to attack Kaido. There's a direct connection between all those events.
It's not part of the Revolutionary Saga, despite having revolutionaries, because once it ends the revolutionary saga is nowhere to be seen. It plants seeds that will influence it, but it's not a direct part of it. At best, it's a pre-prelude.
Dressrosa is its own saga.
Dressrosa is an arc.
It has Luffy beating Doflamingo's direct minions somewhere then moving to Doflamingo himself.
Dressrosa is not formed by separate arcs, thus it's not a saga. Unless you want to say that Punk Hazard-Dressrosa form a mini-saga, but that saga is still part of a larger Yonko Saga.
I could easily say the SMILES and Caesar (who could easily return in a Vegapunk arc) barely had bearing in the plots of Wano or Whole Cake, considering Kaido is not struggling with Gifters and Caesar ended up almost inconsequential at Whole Cake as the gigantism plotline went nowhere and the KX Launcher was a failure.
How can you say Smiles have no influence on Wano? We are surrounded by gifters, Kaido's whole reason to hate Luffy is due to the destruction of the Smile Factory, AND the people and Killer becoming Pleasures is a major plot point in Wano.
Wano simply does not work without all the threads set up in a sequence of previous arcs. Kid, Hawkins and Apoo, the minks, Big Mom being there, the fall of Doflamingo, everything influences Wano directly. Luffy-Law defined Kaido their target way back in Punk Hazard, and everything since then is concluding now. It's clearly an overarching story.
And heck, there's another term that will likely be explored only after the Yonko: Gigantism.
Again, this is seeding for the future but does not making everything a single saga. The difference of seeding and moving the plot is that the seeding plants elements for future stories, while moving the plot leads directly to the next chapter.
Why are those concepts considered "seeds"
Because the element is not directly affecting the current story, its plot is frozen until picked up much later in another story that has its own Introduction, Development, Climax and Conclusion.
but everything else dealing with the Emperors is not?
Because of direct continuation. Big Mom stuff at the end of Fishman Island looked like seeding, but then Big Mom became an integral part of the Kaido story when her pirates went after Caesar in Dressrosa, and again in Zou when both Kaido and Big Mom had direct influence over that arc. And then Big Mom's own arc has an open end that leads her directly to Wano, thus uniting Kaido and Big Mom for the big finale. It's one single story that has introduction, development, climax and conclusion, one arc leading to the other, rather than putting things on hold for a later saga.
We only had concrete details about SMILEs at Wano, with the fruits themselves having no role in Dressrosa at all. And there's away the possibility Wano will intrude in subsequent arcs depending on what the border opening ends up being. Doflamingo's defeat led to the Shichibukai system being dismantled which might lead to this "Revolutionary Saga" you speak of, so wouldn't Dressrosa be directly involved with that Saga?
Compare gigantism to Smiles. Both come from Caesar and Punk Hazard. But Smiles kept being a factor one arc after another, while gigantism was mostly forgotten. Gigantism is seeding: it will be developed in another story. Smiles is a plot thread that directly affects the current story.
When Wano ends, the Yonko Saga will have ended. We may still see Kaido and Big Mom stuff throught flashbacks or consequences of events, but they'll be furthering another story, that will have its own introductory arc, its own developing arcs, its own climactic arc and its own conclusion.