yeah there are some choices I have auto-excluded due to them just not being interesting for my team or plainly bad.

Lantana - just bad, boosting panels are crap.
Azalea, Golden Lace, Purslane and Herbecus Peony all have secondary skills that dont really fit in with my team.

I DO like your Idea with the Yandere girl. I LOVE her VA, though she herself - as I have stated many times before, if this crazy girl came after me I would plant a bullet between her eyes, not wanna risk getting axe murdered just because she is jealous for no reason
On a more serious note though, her ability is pretty good, and would allow the team to put out more damage than expected, especially with Iono and Freesia having the ability to go again in the same turn.

I have not considered her before, because I already had the Slash type slot filled with Nightmare, and have been thinking in terms of Kerria as the Finisher, but I think Kerria would work well as a non-crit nuker in a Crit team. Yes she has evade, but instead of big damage in Evade team, she would do insane damage in crit team.
So yeah, the last spot depends.. Also keep in mind that Tree of 1K whatever ... horrible, long name - does not have yet her Bloomed form. Which I find perplexing, maybe she is not popular enough so she is in the back seat with some of the other less popular 6* ? who knows.

Yeah
Nightmaher, Freesia, Iono, Royal Yandere, X - being any non slash girl
Slash, Magic, Pierce, Slash
Since there is no super good Evade Blunt type girl (only Blunt Evade 6* is Pumpkin and I dont like her Unit type bonus damage thing), the last girl could be of any type until some good evade Blunt is released.