[To me, ever since Misty and Brock left, all the characters the came after them are bland and lacks the charm imo and yes they lack unique personalities well in other words, forgettable. I've seen hundreds of anime but I never seen bland characters like Pokemon. I am sorry if you don't agree with me.
I liked May but she wasn't unique enough, Dawn was ok, but Serena is your typical generic shy girly girl (I am not hating on her though ) and Clemont is sorta just there and he's annoying tbh. Not to mention, Cilan and Iris who were annoying and forgettable as well.
In terms of Ash, well yeah. His personality changes a lot. He is written differently in each region. A character treated this way means the writers are not taking his development seriously. They don't pay attention to quality.
But lets pary Misty comes back and bring the old Ash back lol.
About her popularity, well come one, you can't judge her popularity based on several people's opinion. I know she is way popular in US, and fans made a fuss when she was written off the show, but that doesn't mean she doesn't have any fans in Japan. Again, that figure speaks for itself. They even showcased her Togepi and Psyduck. She is a classic characters and will forever be. ]