I wasn’t clear at first, so let’s put Jasper’s quote into context. “I’ve been fighting from the moment I broke free of the Earth’s crust! [...] Because of what you did to my Diamond!”

Jasper was fighting from the moment she emerged, because of what happened to Pink. That quote alone shows that Jasper was still incubating at the time.

Further proof comes from the exact quote you took from Eyeball: “Kindergartens were incubating their first soldiers” when Pink was shattered, meaning that some Quartz gems were still underground at the time, one of whom, from her own mouth, being Jasper herself.

From a storytelling perspective, it makes much more sense than you’re giving it credit for. It’s already been shown in other ways that Rose was far from perfect - just look at her treatment of Bismuth or her initial non-understanding of love.

Her shattering Pink Diamond not only doesn’t add much to this image; it actually detracts from it in some ways, being out-of-character and making Rose seem hypocritical, both to the audience and to Steven himself (note that in the trial, he guessed that Rose used the Breaking Point).

So there’s not much to gain from keeping Rose as Pink’s killer. So what’s to gain from shifting the blame to White?

First: Obstacles for the current Gems. How would Steven react when he realises that he was doubting his mother for a crime that she never partook in? How would Garnet, who undoubtedly spent years reconciling that Rose shattered Pink, react when she realised it was all a lie? What about Blue and Yellow? How would they react to a traitor among their ranks - their superior, even? The story isn’t about Rose anymore, it’s about the gems and humans and the war between them. This is exactly the kind of conflict that has been used throughout the entire series.

Second: An end to the series. Like it or not, Steven Universe has to end. But to do so, the major conflict between Homeworld and the Crystal Gems has to be resolved. The Diamonds’ current motivation for killing the Earth is for the revenge of Pink, so the only two ways to stop the war are to shatter all the Diamonds (leaving thousands of gems out for revenge), or to convince the Diamonds that the Earth shouldn’t be destroyed. How else to do that than to prove that Rose didn’t shatter Pink, and unite Homeworld and Earth against a bigger enemy?

Third: A plot twist. The show thrives on these. Garnet’s a fusion. Rose shattered Pink. Jasper’s Diamond was Pink. All the monsters were gems. The Diamonds caused the corruption. Ad nauseam. It isn’t like this kind of left-field twist hasn’t happened before with less foreshadowing. Is it really that difficult with the evidence we have to predict that White could have shattered Pink?

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