Unfortunately, the Great Nicholas Meyer wrote his script with an upstart Kirstie Alley in mind instead of the rising star she became; it could've worked if Nimoy was willing to share or sacrifice his screen time like he did with TWOK*. There just wasn't enough room for 3 Big Stars in this struggling budgeted movie and the plot should've been more about Kirk living and learning about Klingons either on a Klingon dominant Penal colony or a community. I was struggling to understand how Meyer thought anyone would be fooled by what he delivered. All of the suspects were openly obvious and all of them were involved, that is definitely not how mysteries work, deception and cunning along with making a character less suspicious makes the genre work.It's not that far away from what you said, actually.
Because the rewrite isn't a simple patch, and I never said it was. Only that when you decide to remove a character from a script, that often means making substantive changes to more than just the name over lines of dialog.
They thought they could just re-assign all Saavik's lines to a brand-new character without doing anything else, and still have the same resonance. They were wrong.
*Nimoy at the time was over with Star Trek and wanted out. He played along but he was less involved in that movie and as sad as I am admitting this, I thought the movie shined because of this because it allowed Shatner to be a star and not worry about screen time politics and other bullsh*t which would return in IV.