There are only 3-4 fights left in Dressrosa and we're done. The fights with the executives are only going to be one chapter (Zoro vs Pica could potentially get 2). The only big plot line left is the destruction of the factory, and that won't take long.
The group on the Sunny and Zou will be handled together and Zou is not going to be long. It was not meant to be. We have more than enough time for this.
One break every 3-4 chapters isn't going to hinder the plot to that great of an extent.
You have no way of knowing the fights will get one chapter each. Since they are more important I can argue they will get more chapters dedicated to them. In the end neither of us know.
I think we will get a few chapters dedicated to what is happening on the Sunny, but then Zou will be a separate but smaller arc. In the end that's another thing we just don't know. And there is no evidence to support your claim that Zou was meant to be a short arc.
Not to mention the world building and any other random things Oda throws in. I personally can't see Wano coming this soon.