A lot of people are calling Kokoro a Top 5, S tier character. Let's examine this assignment.
Starting at the bottom, she isn't garbage like Marie Rose and Honoka, and nobody plays Phase4 so I don't really know where to put her. This puts Kokoro in at least C tier range.
Moving on to the shittier matchups, Brad Wong and Helena are nightmare matchups for Kokoro since they can dodge all her tracking moves with their stances. She also has a rough time against characters who outrange/out-track her (Kasumi, Ayane, Lisa, arguably Mila). Nobody plays Christie right now, but if the matchup is similar to what is was in 5, then that's an awful time for Kokoro as well.
Next we have the commonly viewed as S tier characters such as Hayabusa, Bass (?), Tina, and Nico. Most people generally accept these characters as being busted, and would most likely rate them higher than Kokoro.
The rest of the matchups are all skill matchups in my opinion, with neither Kokoro or her opponent having an objective advantage. People complain about Kokoro a lot but I haven't heard about any specific character matchup with Kokoro that is specifically awful for her opponent, who exactly does she hard counter that isn't a low tier character? I'm genuinely unsure of a single matchup where the other player goes "Oh, I'm playing *x* character and he's playing Kokoro, I guess I just lose."
So going back to the Top 5 assessment: We have two characters that hard counter Kokoro, 4-5 that have an advantage in the matchup, and 3-4 characters that own the top tier rankings. This at best makes Kokoro a Top 10 character, which is also debatable since she doesn't really hard counter anyone (except Marie and Honoka, who are countered by playing actual human beings). Personally, I can probably get behind a Top 10 ranking due to her well-rounded speed, strikes, throws, and holds, as well as her relatively low difficulty. However, Top 5 is a stretch for me since she has garbage tracking, some specifically shitty matchups, and she isn't as mind boggling broken as some of the other characters.