Yamato's joining solves a lot of power level questions and puts things into perspective.
Regardless of how strong she is compared to Sanji, I doubt the crew's original dynamic is gonna change. So he'll eventually surpass her even if he's currently weaker. I think it's only a matter of time before he too gets CoC.
Oda didn't give her a complete 1v1 this arc. Imo that's likely because he's saving her true strength for a future arc. Its the same thing with Jinbe, who like yamato, was also supposedly going to destroy the m3.
Then what happened? Zoro and sanji got power ups, Jinbe didn't, and Oda literally confirmed that Zoro and Sanji are Luffy's wings.
The m3 has existed since east blue and Oda isn't going to break it for Yamato. Next arc Zoro and Sanji will get power ups, Yamato won't, and Oda will yet again confirm that Zoro and Sanji are Luffy's wings.