...If there isn't any opposing force in a conversation, it's not a discussion, it's a chit-chat.
No, Game Freak has not come down and told us their entire reasoning or design process. (If you think art assets, aka sprites and the like, take a few minutes your are grossly misinformed.) But the entire point of a discussion is to figure out why from our viewpoints, and from what we know of others viewpoints. This extends to ruling out other reasonings we think are false, and stating why, with the best of our reasoning ability.
Misty's iconic view is decided by the majority of fans, and what is the most popular view of her. GameFreak understand it goes further than just the games, they've bounced things from the anime multiple times.
Google "Misty", put "Misty" in on deviantart, and put "カスミ" in on Pixiv. That is the popular view of Misty. Tell me the ponytail isn't the majority, therefore iconic.
I've stated why I think the gyms leaders in BW2 have not aged, and why I do not agree that it's for iconic resemblance purposes. I will leave it at that then, if you don't want to discuss it anymore.