I really like Kasha but I think her presence this season has more so amplified that her potential really was with the Season 7 cast on a mainline season. I don't think it's particularly egregious for her to be going now.
She could easily have been High/High in the first two challenges though which would entirely change the dynamic - but the decision was clearly made for Jaymes to occupy the primary camp queen slot and that leaves no room for Kasha (or indeed Darienne really) and both are quickly surplus to requirements for the shows storytelling plans. Plus you have Jimbo who stomps the comedy stuff too.
That's ultimately just a bit of bad luck, as they could have made a decision to turn Darienne/Kasha tension into a several episode arch (one doing better than the other causing jealousy, them 'falling out' under the pressure, make them opposing team captains, one potentially failing to save the other by losing the lip sync, them both in the bottom etc...). Or just allowed either to have a redemption storyline.
But that's not the role they've been cast to play. It sucks for them not to get their flowers, but it is what it is. And to be honest as you say, the next challenge is a Ball, who else is going to be in the bottom if not those two among this cast?
MKD however feels a good choice for a future vs TW series casting, based on how she's done here and how people seem to have responded to her.