3. She knows way too much.
Luffy has already made it very clear that he doesn’t want to know anything about OP or Raftel so Yamato having read Oden’s journal significantly hinders her chances of joining.
this has been discussed before, but let me mention it again: it is irrational for Oden, a Poneglyph writer and reader, wrote anything about One Piece, Laugh Tale, Void Century, etc. in a journal (which is scrap pieces of paper), with normal language. I suggest normal language since everybody can read it and at the front of the journal is clearly written in Japanese kanji & hiragana.
there is not a single mention about One Piece, Laugh Tale, etc. in Oden’s journal. It’s just that Yamato said that the journal has “very important information.” Oden put One Piece info in a journal, which can be destroyed easily, sounds ridiculous. Also if Oden did, which I doubt he did, it would’ve destroyed the purpose of the entire Poneglyph steles, especially Road Poneglyph, and would’ve destroyed Robin’s purpose as the sole Poneglyph reader. Also if that were true, means that now Momonosuke could have also known One Piece location.
and another counter argument is: Luffy spent 2 years of training with Rayleigh, yet Luffy doesn’t even know a single info about One Piece. If Oden journal did have One Piece information, Luffy could’ve just simply ask Yamato not to tell him. This case is pretty much closed
Also if you want to bring the goroawase theory, why don’t you also bring another obvious theory, which is the alphabet theory? So far no Straw Hats have same initial letter.
Luffy Zoro Nami Usopp Sanji Chopper Robin Franky Brook Jinbe
LZNUSCRFBJ. They have Chopper already, whose name has initial letter C, same as Carrot. Even Vivi & Karuu, honorary Straw Hats, their initial letters don’t collide with currently existing Straw Hats.