Random thought I just had about roles in the crew - Luffy recruited Zoro, Usopp, Robin, Franky, and Jinbe not necessarily because of what position he thought they could fill, but because through the course of each arc when he met them, he forged a bond with them through trials of fire like beating a powerful antagonist or saving an ally from captivity. Reread any of those arcs if you don’t believe me; he never seeks any of those people out or pursues them for one explicit purpose other than wanting them to be his friend and travel with him. It may be important to some of the more inflexible posters in this thread, but the captain of the crew really only cares about how he gets along with a person. Think about all the people he’s asked to join - what would Gaimon have done on the ship? What about Bon Clay? Even Kin’emon, a dark horse Sanjidate for some (me), would have no defined position if he chose to leave Wano again.
This is all to explain why arguing that Carrot should join over Yamato because she could fill the (largely unimportant and unnecessary) position of lookout is pointless...first of all, Usopp’s eyesight has always been good enough to see far off obstacles/Nami has a preternatural sense of what physical or meteorological events are on the horizon; second, whether Carrot or Yamato or Joe fuckin’ Schmoe could take on that responsibility doesn’t influence whether or not Luffy wants them to join his crew. Don’t @ me