I think you need to refine your comparison just a little. It is not fair to compare a 7-day Princess or RCI cruise to a 10-day or longer cruise on Celebrity. My own experience tells me that the differences between similar Celebrity and Princess cruises is minimal unless you are in one of the top suites. Princess is more relaxed, Celebrity has more refinements that sometimes border on pretentious.
If you wish to make comparisons with Princess, it is best to seek the advice of those who prefer the Sun-class or Coral-class ships and have some familiarity with Celebrity. It would be interesting to see what Celebrity would do with a 2500+ passenger ship running 7-day jaunts, and what kind of atmosphere would prevail. Horrifying perhaps, but interesting.