I'll get back to you in a couple of weeks, Mikan. It should be fun.
Thank you for addressing all my points: Luffy hates people who abandon their nakama; even when Oda was given the opportunity to show her depth, he continued instead to make gags about her selfishness; Perona's character hasn't been set apart from other reoccurring minor characters.
Yeah, Oda could give her a backstory, could have her mature. But going by what we have now, there's no foundation. At every opportunity, Oda has just played her for gags. Perona has shown no depth, has no connection to Luffy, has no special skill they need, has no dream that could be fulfilled with the SHs, and no reason to join.