yamato did quiet a bit that required their character, holding kaido for the time they did was still important when zoro and sanji were busy on their own and macro clearly wasn't in a state to do that. i would have loved another straw hat to handle it but they def wouldn't have held their own. I don't see how you write around that though if this is how oda wanted the fight to work out where there are multiple rounds.
Outside of that yamato was given a backstory connected to the roots of the story being told in wano, I hope they join because I want to see them in the story and the interactions forward. the character is incomplete. and I find it idiotic for oda to setup a fight with greenbull and have momo "prove" they can handle people but then yamato stays who was not included in the battle because of their want to join the crew.
Yamato needs more development but I don't believe its impossible, the character is basically the same level of completion as jinbei while carrot never even had much of a character. as well tama is too young and even buggy and shanks didn't go on the trip to laughtale.