The only box office "symptoms" one might detect are regarding the trajectory of interest. Anyone who defends the quality of TLJ based on its overall box office is delusional. We won't know if TLJ is a failure until Solo and, more importantly, ep. 9 come out. Let's look at (what should be) a less controversial example: The Matrix trilogy.
The Matrix: $463,517,383 Worldwide
The Matrix Reloaded: $742,128,461 Worldwide
The Matrix Revolutions: $427,343,298 Worldwide
Many people feel that Reloaded and Revolutions were an artistic failure, that ruined the mythology. Does anyone think that Reloaded was a better film than the Matrix?
I'm sure there are some. However, the consequences of artistic failure don't really hit the box office until the following box office. I can almost guarantee you that Ep. 9's box office will make The Matrix Reloaded look enviable, in proportionate box office failure. Either way, that's when we'll know how pervasive fan disappointment with TLJ actually is.
Box office is only a gauge of momentum, in a film's ability to outgross their predecessors.
The Force Awakens: $2,068,223,624 Worldwide
The Last Jedi: $1,235,274,584 Worldwide
We know that The Force Awakens had a lot of momentum behind it thanks to the popularity of the franchise, but failed to sustain the momentum of franchise popularity. Sales are down, not up. Can a sequel make more money than its predecessor? Here's a list of films that have:
https://en.wikipedia.org/wiki/List_of_film_sequels_by_box-office_improvement