you're right, every time someone catches up to OP they kinda go into shock when they have to transit into reading it weekly, I've seen it happen many many times over the years, especially when people are used to judging chapters on a ''week to week basis'' or '' chapter to chapter'' if you will. Oda however writes the Arc (and the story) as a whole, not as each individual chapter, that's why his Arcs should be judged once you have the volumes and can read through them in one go. It's also why you shouldn't judge Sabaody on teh Duval stuff and the Sabaody Park fun chapters (which lasted about 20 chapters = half a year), you shouldn't judge Thriller Bark on the funbeginning chapters (which lasted more than 20 chapters), Water 7 also had many chapters like that, ...
it has always been like this, take it from a fan of 11 years, but no matter how ''slow'' parts of OP arcs may get once teh Arc is finished and I get to read it as a whole I always love it becasue that's how manga should be, not to deliver exactly what you want every week but to deliver story that ultimately ties up into one single story (arc), each chapter isn't a stand alone, it's simply one little part of the entire story
sometimes I though newer fans would have an easier times if Oda published Volumes instead of chapters, but that would really suck for me