Would you not agree that KOTCS is at least considered a huge disappointment (if not downright hated) by many/most? Maybe even by the "majority"? Then please explain its 78% RottenTomatoes rating, A-/B+ initial CinemaScore and nearly $800 million worldwide box office take.
Unless you're going claim that KOTCS haters are the "vocal minority" you're probably going to have to reconcile that somehow in comparison with TDKR, which fared a little better in these areas, but not by much. Or maybe admit that these numbers really aren't indicative of a film's overall critical reception, especially after the passage of time.
TDKR and KOTCS have some pretty significant differences, statistically speaking. For one KOTCS was part of a legendary Lucasfilm franchise following a 19 year drought. I'm not sure how accurate a Cinemascore rating would be for something like that. If I remember correctly you yourself had to take days to decompress after seeing it. It'd be nice if you could compare a movie that wasn't SW or Indy just because those franchises are SO beyond the norm with regard to audience anticipation/reaction.
But let's go with KOTCS anyway since you brought it up.
Rottentomatoes critics:
KOTCS: 78%
TKDR: 87% (higher than Batman Begins)
That's a pretty big differential. Nobody gets a C+ on a test in school and says, "oh that's basically a B+."
Rottentomatoes audience:
KOTCS: 59%, 3.4/5 average rating, 1.1 million votes
TDKR: 92%, 4.5/5 average rating, 450,000 votes (and also higher than Batman Begins)
Huge disparity. I certainly won't concede that TDKR had a similar reception. If you can find a movie that we can agree is a "disappointment" that got an A Cinemascore, 87%+ rottentomatoes, 90% audience rating AND made a billion at the box office then I'm all ears. But I don't see KOTCS as fitting the bill. Revenge of the Sith looks to be a better comparison but again it's SW and still has a KOTCS-eque audience rating on rottentomatoes compared to TKDR.
If the website stats don't mean anything then it shouldn't be that hard to find other movies that were critically acclaimed, made tons of money, and yet still are generally considered to be disappointing or subpar. And before you bring up Titanic or Avatar people who hate on those movies really are just "backlashing" against the hype. They're both still very good movies even if the level of their accolades makes us scratch our heads.