My opinions may differ from a lot of those here, but in my experience:
Kasumi
Pros: Very fast, good combo chains. Great distancing and mobility, allowing you to play a good defensive game as well as offensive.
Cons: She's played a lot, so players will often memorize her moves for counters. Sometimes her kicks will leave her exposed to whiff punishment, as well.
Before, "in your experience" (in another thread) she was slow, well not that fast as you put it, now she's very fast, lol. Kasumi does not play the distance game very well. So I don't know where you are getting "great distancing" from. Her being mobile, whatever that means, ok. Which kicks exactly leaves her open for whiff punishers? That's an extremely general statement that can actually be applied to any attack that's being whiff'd. I also don't know how a character being played "a lot" is a con. Never stopped my success with her no matter how predictable she is.
Lei Fang
Pros: Good high-to-low variation.
Cons: Bit slower than some other characters. Juggling will be more difficult without practice.
Leifang has good high to mid variations. Not high to low, that would be Zack. Leifang's low game is nothing special, it's a decent option to poke with but that's about it. Leifang is not the fastest but she's not slow either. She is faster than a "bit slower than some other characters." though. All of her initial jabs/pokes are i10, i11, and i14. That is about average for characters. Yeah, I am pretty sure juggling without practice will be diffiuclt, that's not neccessarily a "con" but is a part of character difficulty.
Kokoro
Pros: None
Cons: None. Kokoro's not great in any particular area, but she's not horrible in any either. I think that's why you rarely see high level players using her, is because beyond the basics, she doesn't really offer anything unique.
Everything I told you was a pro for her. You put "none" for her as a pro. So I don't know how I re-stated anything you said. You said she's not "great in a particular area", she may have the best whiff punisher in the game. Her whiff punisher is safe, puts the oppenent in an sit-down stun putting her at +25 and it has great range. I don't know the speed of the attack. But that alone makes the move pretty unique and her particularly good at whiff punishing. In 4 she was the safest charater in the game, and I am pretty sure she's still up there in 5 if you exclude the VF characters. But she's still pretty safe more than what most charaters are. Kokoro has PPgrab strings other character have to free cancel to pull that off, she has them in her movesets making it hard to defend against when players implement it correctly in her game play. She also has an unbreakable chain grab something that only a select few characters have. Then you finish by saying, "she doesn't really offer anything unique". I mean what else more do you need for her to be unique besides the few thing I just gave?! She has more stuff to her as well, these are just a couple highlights.
Though, I am just "re-stating" everything you just said. When you literally said nothing about her.
This is also not the character discussion thread. So I will not be commenting on any further that you have to say about this. You can PM me if you care to continue.