For the original trilogy, ESB did 80% of what ANH did, and ROTJ did 74% of ANH
By comparison TLJ did 64% of TFA and TRoS did 52% of TFA. That is much more of a drop than just the "nature of things" when it comes to sequels.
Also very often when it comes to popular movie series they will have big $ for the first film, lesser for the middle film(s) and a big boost for the finales as people get excited to see how things wrap up. The prequels did $924m, $645m, and $868 respectively. Similar results for Indiana Jones, Harry Potter etc. Or for LOTR each movie increased $ as it went along. A finale of a trilogy, and in this case a saga that spans many generations, albeit being profitable, to do as poorly as it did in context to what this series is has to be heavily concerning.
As for your second part, I simply would have preferred that they had a coherent start to finish story and not "make it up as you go along" from movie to movie constantly changing course/direction. It might have been bad if their start to finish story was crap, or it might have been good. We won't know but I suspect it would have been received much better since it would have flowed more coherently from film to film.