Oda will never break the monster trio. It has been a core straw hat dynamic since the beginning and wano has basically proved that. For years people said that Jinbe would break the monster trio, but did that happen? Nope.
Oda deliberately restrained jinbe from joining for this very reason. He could have had jinbe join in FI, Dressrosa, or Zou. Did he? Nope. He wasn't officially introduced as a straw hat until wano, where Sanji got a raid suit and his lineage factors; with him ultimately taking on a calamity whereas jinbe high diffs Who's Who.
It doesn't matter if Yamato>Sanji, Oda isn't breaking a core dynamic of the crew for yamato. The options in regards to her are this:
- Yamato never joins the crew
- Yamato joins at the end of Wano, but is weaker than Sanji
- Yamato joins the crew in a later arc when she is weaker than sanji