Revelations from Patch 7.2: Seekers of Eternity

[Thighland]

I mean, she spent several centuries doing exactly what Calyx needed of her, and 7.2 showed us that Calyx is a 'learn from failures' kind of person more than he is a 'plan for all eventualities' person. Why throw her out if she's doing everything needed of her, and the event that she goes against him both hasn't happened yet and, as far as they know, very well might never happen? That just sounds like a whole lot of needless work to produce a perfect plan that you don't need, because the current one's already working just fine.

Learning from failures is fine, but you must agree that there are failures so great, that there's simply no excuse for them. Losing the key is almost the worst case scenario for Calyx' plans; one of the last things he should've wanted to happen. (Remember: He has waited hundreds of years for this key, and that he got it back at all was actually just an insane coincidence)
There is a difference between failure and catastrophe.
For Example: If you found a button that could destroy the earth, would you hand it to the equivalent of an emotionally unstable teenager? Of course you wouldn't, because everyone knows that is not a good idea. There is nothing good to be learned from doing that.

If you introduce a character to a story that is a scientist, driven by intelligence and logic, every time that character does something illogical, it's either a writing mistake, or a plothole that needs filling.
I can accept that Calyx' plan might not be flawless, but if that is the case, the story should shine a light on it instead of making us guess about these supposed flaws.
And that is all I really want in the end, and I really hope 7.3 delivers. There is a good chance that Sphene's crown will tell us more.

And similarly, why go through all the effort to use the regulators to manipulate people's memories to achieve a plan without Sphene, when 'get Sphene to ask someone to do something' has worked for hundreds of years? Hell, I'd argue that the existence of Oblivion and the largely-undiscussed people not using regulators shows that trying to change their approach is really not feasible; he actually can't control the memories of the entire population. However, both Oblivion and the non-regulator-using masses seem to like Sphene well enough, at least as far as they ever could like someone in her position, so why would you ever stop using her as the figurehead and risk escalating them into action? You call the idea of Calyx replacing Sphene 'pragmatic', but I actually think it'd be the mark of an irrational and paranoid actor to replace something that's worked perfectly for centuries simply because, in some unforeseen circumstances, it might backfire. Especially because there's absolutely no guarantee that your replacement plan works any better, and that the act of replacement itself could very well cause great issues.

I'd argue that there are ways to replace Sphene and manipulate the masses' memories without stirring too much trouble (seeing as the Alexandrians are probably the most docile people we've ever met), but we'd get massively off track that way.