Yes, there are legitimate gripes behind the attacks on Kennedy. And, yes, there is blistering misogyny behind the attacks on Kennedy. There is also filthy racism, and just petulant "that's not the way I wanted it done" behind the attacks on Kennedy.
I doubt that we could assign percentages without an in-depth content analysis of all social media and press publications on the topic. Even then, genuine motives might be hard to assess (how many "legitimate" comments are actually being fueled by something else?).
That said:
There's no doubt that there are troglodytes who want only their vision of Star Wars, and who feel entitled to abusively scream bloody murder if they don't get their way.
There's no doubt that a substantial percentage of those troglodytes' vision of Star Wars is very male, and very pale.
There's no doubt that Kennedy brought a vision of Star Wars to the table aimed at females (who are out performing young men in both admission to, and graduating from college in the US, and who thus represent an attractive long-term target for Disney).
There's no doubt that if a franchise as beloved, and as expensive to acquire as Star Wars ($1 Billion for the LucasFilm deal, wasn't it?) begins to falter, whoever is running the shop is going to take heat, both among the fans, and in the C-Suite.
There's also no doubt that one person rarely screws up a film or a franchise. If Star Wars is stumbling (and I'm not yet convinced that it has, Solo's performance being possibly a blip rather than a trend), it cannot be solely Kennedy's fault. Yet neither can she be faultless.
So, does she deserve some criticism? You bet.
Does she deserve everything coming at her? I doubt it.