I should have had over 1k AGI with Leaf's Ring, but my trouble was that I was using the +5 Drake Sword and I didn't have any extra turn equipment other than an unupgraded Andor's Sword. Rapunzel was a bloodstain when I got there because I lost to Behemoth. Did it again a second time after upgrading my other equipment and clearing route D, and completely rolled those two bosses with Power Within -> Ruinous Storm.
EDIT: Power Within into Heavy Soul Discharge makes me feel like goddamn Saitama
EDIT2: Theorizing the backstory of BS1...
I think the world was originally a fantasy fairytale world where characters co-existed, but somehow at least one eldritch abomination, Shub-Niggurath and her Younglings, managed to enter/appear in it. Either they have always been lurking, or a summoning went wrong and brought them in (evidence of the latter in Glinda's diary, possibly).
Of which, one of the Dark Young was especially interested in the Author's fairytales, and managed to change the world according to her twisted interpretations of the fairytales, rewriting personalities and stories (merging Snow White and her Stepmother, etc). She even managed to trap her own mother in the world as Baphomet, and took on the moniker as Mary Sue, the god of the world.
Mary Sue would constantly watch the world from her self-made safe haven, erasing anyone who got close to the truth of the world. The only ones she seemingly could not/did not want to erase were Red Hood, and later, the Author/Protagonist.
The Author fought against her corruption but lost his memories and body, before being saved by Alice to become the Protagonist. Mary Sue, bored, decides to let the MC roam free to see if he would find the truth, and then crush him afterwards as another of her twisted stories.
In Ending A and B, he never gets to the truth, and the corrupted world simply continues playing out, with Mary Sue pulling some strings to ensure his despair.
In C, he seemingly successfully destroys the corrupted world, making it look like a "True End".
As for the ending of D... I'm going to guess that it's linked to BS2, making it either the True "True End" or hinting about what would happen past Ending C. Perhaps the "Alice" we see at the end is yet another eldritch abomination... (Don't spoil me on this)
If there's any confirmation of the backstory anywhere that isn't BS2 spoilers, hit me up
No spoilers regarding BS2 just my opinion on C and D endings.
I think you are on point but I would like to add that after you beat C end and do Leaf's end again you will see a continuation that she describes as a love letter to you. Also after you beat C ending and talk to her again in Holy Forest before going to a NG she has a one time dialog that hints that you actually beat her but the world was reset to before that. IMO C end ist just another one of Mary Sue schemes thus making the D end the only ending where she didn't actually planned, also I don't think Baphomet is her mother cause if you talk with leaf outside Lost Empire she will ter her mother if The Fairy Godmother who gaves Cinderella her whishes but that could also be another one of her lies.