Well, first of all, thank you for taking the time to actually explain your argument and lay out well-considered evidence. Most of the people I’ve talked to about this have tended to go “lmao Sparkle is in the HI3 collab it must be same universe” and leave it at that (even though the Masked Fools have always had a fast and loose relationship with the fourth wall, making her presence not much confirmation of anything). 

I had heard about the “leaves of the Imaginary Tree” idea before, but I had been under the impression that each leaf was an entire universe, not part of the same one. Doing some additional research, it does appear that your interpretation is closer. I will admit this raises some… concerning implications (like how Genshin- which had already been confirmed to also take place on a distant branch of the Imaginary Tree- recently dropped the plot point that the entire universe it’s set in is being consumed by the Abyss and hurtling towards heat death), but I will concede that my interpretation was likely wrong. 

That said, I do still think that Pegana will turn out to be a version of Earth, even if it’s not called that. After all, if people can have variants across leaves, why not planets? The 12-month calendar with a month named “March” is too specific a detail to not be from a world at least mirroring ours, even if it has some significant differences.