Kiki is considered the center of TF, but I don't think her singing is better than Risamaru or Kishimon. Even Karin's voice is not considered number one in J=J despite being an ace. Kiki may be among top dancers in TF, but I consider Maopin number one. One thing is that she's very balanced between Singing, Dancing and Visual, and draws fans the best . That's how she's the center. UFP never considers center position equal to being better than other members at all skills. Being the most popular isn't equal to being the most talented.
Yes, I don't like when Risamaru badmouths other members on SNS, regardless of the situation. It's not what fans want to hear. I even agree that she shouldn't come back since it would benefit neither her nor the group. However, there is one thing that I consider true about her: She works hard to earn her center position. I don't know how much she lies or fakes, but singing skill cannot be faked. Mizuho also worked hard to earn her center position, and the statement by Risamaru that Omizu doesn't deserve it (based on the proof we know) is false.