Jinbore does nothing other than acts like a follower. Of Tiger, of WG, of Big Mom, of Whitebeard to finally settle his whole existence into worshipping Luffy. Which he btw left his crew for. He keeps switching alignments faster than epilepsy.
His sole existence is to keep saving Luffy's life for no apparent reason other than being there. That is why he's recruited.
Now Yamato isn't the best written character, but there's space for her to grow and she would fit in with the crew cause she actually has a personality and is fun.
Jinbore is like... Personality-less old man (in comparison to the rest of the Strawhats) who doesn't really fit in with the rest. We could say the same for Brook, but at least he's got a bone body yohohoho