If there was one thing that the modern day Flash was determined to do before it bowed out, it was introduce audiences to a new character that they just couldn't get behind. And when I say "determined", I mean determined.
Khione was the remnants of a season 8 storyline designed for the ninth season at a time when the creative team weren't aware it would be the show's last. But upon finding out that it was, they decided to proceed anyway, and the results were, well, not good.
Long-standing Flash character Caitlin Snow's attempt to save Frost saw her step into a chamber that was supposed to bring her back. Out stepped Khione, revealing that Caitlin had essentially died and this new character had taken form. Naturally, this rubbed fans up the wrong way but not nearly as much as the fact that not a single character shed a tear over her apparent demise and actually went out clubbing because "it's what Caitlin would have wanted". Sure.
Anyway, Khione herself offered little of value to the show. She was seemingly a goddess of nature who possessed limitless powers at one point, and then completely powerless at another. When she did finally reach her potential, it all happened off-screen during a time jump. And to top it all off, Caitlin returned in the series finale alive and well.
With more development and a little care, Khione could have been an intriguing new addition to Team Flash; a wild card for the show, perhaps. But here, she was just in the way of the show's final storyline, robbing screentime and development from Caitlin, all while accomplishing absolutely nothing.