I never understood reasoning behind claims "pre or post Togepi Misty" because there is no such thing. We are talking about same character and not two different creations of fiction, nor i understand why is division made in first place because Misty as character never had such shift to the point of being unrecognizable.
Thanks to development Misty only changed for better. From character in narrative it is expected that they grow, change, go somewhere with their story instead of staying completely same since their introduction. There is no point to such character being recipe for ending up at some point incredibly boring and stagnating, with people growing tired of same old gags and quirks repeated all over again(like they did with Brock in DP).
If character develops it doesn't mean his personality disappears, but it means his personality changes. Same goes for Ash maturity in Hoenn or Mays at end of BF , they evolved as characters becoming more competent and independent in their own right becoming less impulsive or in later case ditzy, changing just like people in real life do and i never met anyone saying how this growth made them "boring".
Same thing happened to Misty. When we met her she was abrasive, quickly tempered erupting over every little thing having to grow up in older sisters shadow and prove herself to everyone. Over time past Kanto we saw more of personality being showed under that rough surface which allowed for significant development later down the road. She gradually started to mature and grew out of sisters shadow and complex of feeling inferior in looks, skills and everything . She became more open to Ash and Brock sharing with them her history and growing to value friendship she had with them much more ,learned how to better cop with responsibility and bond with her pokemon eventually becoming more confident and stronger as trainer making steps forward in career of becoming water master which was showed in Whirl Islands. She also overcame childhood trauma from Gyarados capturing it becoming at end of day more independent character while keeping enjoyable traits remaining quirky and tomboyish with writers eventually finding right balance between tough and softer side .
People often like to associate slapstick from early Kanto with Misty not realizing how hitting people in head was just slapstick humor and not defining trait of character, his personality. It was just gag which got cancelled in mid Kanto for other characters too, not just Misty with artificial objects like paper weights or mallet never being used in new sagas.
There was much more to Misty character than just smacking people heads and i for once liked change because it expanded more on other personality traits which were often overshadowed by that .
Post Togepi Misty how some like to call it was still full of competitive streak, snarky liking to make jokes about Ash, flirty zooming around several boys they met, passionate about various hobbies like Cilan is(fishing, water types, cute pokemon), deep romantic trying to get other couples together as showed in Nidoran episodes from OI, couple from Whirl Islands and guy with Ssndslash etc and full of enjoyable traits. But she was also much more confident, independent and outgoing as we saw in Hoenn becoming stronger as trainer and person. She still has temper too, but compared to early days she is less violent and i don't have any problems with that because you don't need physical abuse to create entertainment when characters argue or try to out play each other.
I will say it now. I enjoyed in Misty in late Kanto, Orange Islands, Johto and hosos in Hoenn a lot more than i did in early Kanto because aside from temper which was still showed we get chance to also know other sides of character and personality traits becoming more profound.
I prefer characters which develop, go somewhere or to draw parallel. I like dishes with more texture and layers added to it, hence why i appreciated character development which Misty received .
I wont deny she was still poorly developed in story sense not being done much with her goal and ambitions, bu as character she wet through struggling, gave us insight in hr own personal problems with writers doing good job in that aspect of development. More than i can say for Iris.