Rafe's "But she doesn't have enough to do in the books for someone like Sophie Okonedo to do justice" argument would be so much more believable, if just for starters there wasn't a in-narrative plot conceit that would have justified re-casting the actress, if it was absolutely just an actor availability issue.
They could have recast with another brilliant, talented unknown who could capture the spirit of the character, and kept telling her story. JUST FOR STARTERS
But it would have been so much more believable if he hadn't LITERALLY STOLEN PART OF SIUAN'S PLOTLINE FOR THE REST OF THE SERIES, and given it to his white lead instead, last season, re: coping with lack of purpose after being 'stilled'. That should have been the biggest red flag, I just kept tricking myself into thinking it would be a narrative parallel, instead of a narrative burglary.
It would be so much more believable if Siuan's actual narrative for the rest of the series wasn't just about her playing washerwoman but about her being an political power behind the scenes and subtly whipping the Salidar rebels into shape, clawing back from utter despair and the disdain of everyone around her,and being a crucial mentor for Egwene, (sometime they're stealing and giving to another character, again)... except in S3 they chose to portray Egwene as actively disdainful of her, and Siuan as spectacularly inept politically and practically deserving of her own downfall in how badly she bungled everything.
It would be so much more believable if Siuan's actual narrative wasn't about her wanting to drag Elaida down because the coup was about LEGITIMATELY IRRECONCIABLY POLITICAL DIFFERENCES and they hadn't chosen to have Siuan toy with Elaida's exact position about caging Rand in order to, again, serve Moiraine's storyline last season, only to reverse course without a single explanation of what changed her mind, and have it not even be relevant because Elaida's seizing power was more about their petty personal beefs, than the fate of the world, in a way it wasn't to the same degree in the book.
It would be so much much more believable if we hadn't had to sit through three goddamn seasons of invented scenes featuring Liandrin, who was a two-bit antagonist in the book getting endless screentime, backstory, and motivation (including at the expense of other characters including Nynaeve getting robbed of her confrontation with Moghedien in the finale) proving how capable they are of coming up with things for an actress to do, if they want to keep her around...
Or even worse, Maksim, conveniently played by Rafe's boyfriend getting plotlines, character development, and practically as big a role in the Battle of the Two Rivers as Perrin himself, (including that being at the expense of another black queer character, Ihvon) when he was a glorified background extra in the books who died off-page.
And that's not even getting into Moiraine being treated far more as a protagonist and getting significantly expanded development, screentime, etc. (A decision I absolutely adored, for the record, but it's hard to deny that often seemed to come at the cost of Siuan's own individual narrative, including literally as I already said when they stole Siuan's stilling plot to give to her, and something made even more blatantly clear when Siuan's death scene was used as character motivation for Moiraine.)
It would be so much more believable if the show hadn't inexplicably decided to spare Leane from the same fate, apparently to give her part of Siuan's narrative too, when she was an even more irrelevant character in the books, whose narrative had even bigger problems re; misogyny.
At the end of the day, it would be so much more believable if they hadn't demonstrated time and again just HOW MUCH they are capable of altering the narrative and giving greater depth and empathy to a number of characters, and changing their narrative role within the story, when they want to.
They absolutely cannot use 'but in the books' as an excuse when they've repeatedly, gleefully chopped and remixed the narrative in service of the story they wanted to prioritize telling.
Siuan's story clearly wasn't a part of that set of priorities. Fine.
But they absolutely could have come to Sophie with bigger ideas rather than getting her approval for the character's slaughter based on their own lack of imagination for how her storyline in the books could have been enriched and transformative, or again, gotten her blessing for the role to be recast, if she was totally unable to commit to it.
The failure to do either is a DECISION they made, not one they were forced into, and they need to own that, as well as the fact that their priorities have frequently seemed to not include their black actors, to the same degree.
I could go on, but I need to go wash dishes.
It's just shitty writing that treats a complex queer black woman's story as ultimately disposable and worthy of being chopped into pieces and redistributed, with a vague promise of her maybe coming back later in only her narrative capacity as Moiraine's love interest, as if that's sufficient compensation, and I don't believe a word of it.