A. There's a world of difference between comic books and novels and major feature films
B. Diversity is not responsible for the criticism's directed at TFA, TLJ and RoS. Some of the flaws were simply trying too hard to cram all the popular elements of star wars into a series of 3 hours movies, some of it is filmmaking style, and some of it was executive meddling with the script and final release instead of standing back and letting the director do his job.
Note that sequel after sequel after sequel from all franchises tend to suffer from this. No doubt that Star Wars popularity, name recognition and hype led to the flaws being magnified in public opinion.
C. Diversity is about reaching out to underrepresented demographics - i.e. women, people of color/minorities, and LGBTQ+; for inclusion in staff, and inclusion in 'casting' and inclusion in 'character.' This doesn't mean that the entire story will now focus exclusively on the "diverse" character, but rather it will enhance the story by adding a new perspective, a new lense to view things. And in the greatest tradition of art, it will borrow a bit from real life backstories represented by this diversity and weaving them into the narrative.