So your little pea brain can work out any of the following scenarios?
- Yamato does indeed help against Aramaki, he gets stalled enough so that SHs escape and Yamato still joins last second
- An unexpected third party arrives and helps deal with Aramaki while the SHs leave... with Yamato
- Momo strikes a political deal with Aramaki and the WG at the last second
- Any other possible outcome from the shitton of possibilities
Yamato appearing in this chapter was precisely needed because:
1. No Marine knows about her, and specially not about her relation to Kaido. She just spilled the beans to Aramaki at the first chance.
2. Aramaki measuring her strength by taking a few hits would serve so that he can inform Brannew about her threat level.
3. He also needs to be shown that she's a free agent
not related to Wano.
Both of those factors are explicitely shown because they will be needed when the Marines, based on Aramaki's report, give Yamato her shiny first bounty.
But you wouldn't know because you're still taking Math IV or some shit.