Hitomi's 2F+K is i19, Kasumi's is i20 and hell, Helena's 2F+K is i23. Do you honestly believe Kokoro's being 1-3 frames faster makes a significant difference? Combined with it being high/low and non-tracking, it should be faster. You aren't countering a good use of the aforementioned tools on reaction consistently, the animations are too non-descript.
7K when at -4 makes it i16, easily beaten out by jabs, 2Ps and 6Ps. The people that complain shouldn't be listened to, simple.
Yes, it does make a difference. Helena's is 23 frames, but the animation is easier to see, and that helps. It is also slow escapable, only allowing 6p as a follow up. Hitomi's low may be 19 frames, but if she hits you on normal hit, and you slow escape, you are at +1. Kasumi's low kick is also slow escapable, allowing no moves to connect afterward. Kasumi's and Hitomi's lows also don't have a follow up after them, and even though they are standalone moves, they are mostly done at the end of a string, making the mix up more obvious.
I personally don't have a problem fighting against alpha's 7k, but I hear the complaints, and when I use her, her 7k will still beat out counterattacks. The move isn't a poke. It does 62dmg on counter hit, and should leave her at a greater disadvantage on guard.