Not quite, as much as it pains me to go against this.
TAV had not only the secret ending though, but also the FM+ insertion of the Lingering Sentiment. The fight being non-canon aside, Nomura gave grave importance to the LS's words of "him" not choosing Sora for the Keyblade, indicating that Terra was the one who chose Riku for the Keyblade.
Yes, had Riku been the chosen one and Sora just snatched it away, I'd have agreed, but TAV, unlike Xion, have been displayed in the original KH2, and beyond that - for better or worse, referenced in the FM+ with direct relation to Sora and Riku.
I agree about Xion having importance on KH3, otherwise I fail to see the point in them bringing her in (the mere relation to Roxas in light of Ven existing gives her such importance, not to mention Xemnas with his probable relations to Terra being the one that brought her in), but unlike TAV, she was never ever even referenced (unless I'll get my wish and she's Aqua in some form, which means that once Aqua was shown, so was Xion).
Overall you're right, but you're also very, very wrong.