Zoro has better feats than Yamato, I'll explain why when the chapter drops.
For now, I'll just say this, Yamato joining the crew doesn't change the core dynamic of the crew that Oda spent years building.
Yamato is not Oden, nor is she joining the crew the same way that Oden did. If Yamato joins the SHs, she's going to be a permanent member much like any crew member while Oden was borrowed for a specific purpose. Also, Roger's crew doesn't have the M3 dynamic. Gabban may be the 3rd strongest Roger pirates, but they work differently from Luffy's crew. Rayleigh, for example, officially held the highest rank after Roger. Oda did not bother disturbing the dynamic with Roger and Rayleigh for Oden.
For now, I'll just say this, Yamato joining the crew doesn't change the core dynamic of the crew that Oda spent years building.
Yamato is not Oden, nor is she joining the crew the same way that Oden did. If Yamato joins the SHs, she's going to be a permanent member much like any crew member while Oden was borrowed for a specific purpose. Also, Roger's crew doesn't have the M3 dynamic. Gabban may be the 3rd strongest Roger pirates, but they work differently from Luffy's crew. Rayleigh, for example, officially held the highest rank after Roger. Oda did not bother disturbing the dynamic with Roger and Rayleigh for Oden.