I believe in Oda's writing credibility to explain and express clearly why she was actually needed to be in the arc than you making something up like diversity when you already had 2 Minks in the story that had established roles to be where they were. The simple fact is that, if he didn't want her around and was irrelevant, she wouldn't simply be there. I feel this because I know that Oda's improv and creativity has shown throughout the series.
Case in point:Hence why saying Carrot was simply there for character diversity is a poor excuse as Oda has done a lot more for characters with very little time. If she had a reason to go to Whole Cake Island prior to Chapter 877, the story would have made that clear. That's why I told you her exclusion from the narrative is strange, as she doesn't progress it, provide exposition, or is at the center of conflict, yet she's always here. For no reason that the story has addressed.
- Vivi wasn't originally supposed to be the princess of Alabasta. He just decided that Miss Wednesday could play the role of a princess for the Alabasta Saga based solely on the fact with her hair down she looked like one.
- CP9 were originally going to be random government agents, but Oda decided to make them the Shipwrights (Lucci and Kaku), the Secretary (Kalifa), and the Bartender (Blueno) to add drama and make the arc more interesting.
- It is common knowledge by some of us that the 11 Supernovas concept was literally made up at the last minute because Oda's editor at the time said the arc felt boring. Many of them became popular because of their unique designs and cool personalities, the most popular being Law. So Oda expanded on this character over the timeskip and made him have a lot more depth and personality, which made him popular. So popular he stole Zoro's #2 spot on the 5th popularity poll.
- As minor as it was, Cavendish care and relationship with his horse, Farul, was suggested by an editor and he went with that, a character he already established.