Out of curiosity, what are some movies that had a mixed reception that you consider to be 'the best'?
FIrst ones that came to my mind are Hereditary, Midsommar and The Lodge. I remember sitting in the theater, absolutely loving these movies, whilst the audience around me was loudly laughing and proclaiming how terrible they were. Definitely made me realize that general audiences tend to like in-your-face, jump-scary movies, rather than deeply unsettling and disturbing movies that require you to pay attention to the details.
As for RottenTomatoes, I think it always mattered to a degree, but it was the release of The Last Jedi and Captain Marvel that really turned it into a battleground of ideologies, where if the score didn't match someone's personal opinion, it was 'brigaded' and 'fake' and an indicator of someone's political beliefs. Been a mess ever since.
Those two films and the critical reception to "Dave Chappelle: Sticks & Stones" made me realize that RottenTomatoes should not be taken too seriously. Overall it can be an indicator of quality, especially the audience score, but above all you should make up your own mind.