>>34812476It's not. It's just that her voice is unstable, her control can differ from one karaoke to another. But when she's at her fittest you will hear one of the best voice in Hololive.
Her performance in her 3D showcase and mini concert were among her worst, /risu/ was in shambles back then. But she was at her best during Youtube music weekend:
https://www.youtube.com/watch?v=5kb7skBq8bY