I've been saying
Zoro and Sanji get CoC vs Sommers and Killingham
Then Shamrock and Garling show up and give them a real challenge, and let them test their CoC against others that have it
We've got an evil Dad who makes his son's into soulless warriors and killed his wife, and a dude who's Sword has Three Dogs/Swords in it. Dog Swords?
Garling and Shamrock were made for Sanji and Zoro.
Again, I maintain that if the WG starts bringing EVEN MORE people into this situation, if should solely be a display of overwhelming force to one sidededly crush our side and functionally win. There is literally no reason to just piecemeal bring one or two people here just for them to ALSO lose, extending the arc more for no actual purpose. If Oda wants to bring reinforcements then he should just have Shamrock pull up with the whole HK roster (to introduce the current day HK's squad properly), and some of the Gorosei (or as you said, maybe at least Garling) and they just overwhelm us and run us off the island.
Otherwise, what would be the point? Just to give Sanji and Zoro opponents that are more of a challenge? That's boring, and doesn't really serve the plot imo. I don't think Zoro or Sanji would really stand a chance of beating Garling or Shamrock right now regardless.