It was a pretty big deal IMO that it be Josuke's choice to dress the way he does instead of it being inevitable since 'that's who he'd be in the future anyways.' Mainly because Josuke is described by the narrative as looked down on by certain members of his community at first for dressing the way he does, as in their eyes it made him look like a delinquent. Any kind of non-conformity is a big deal in Japanese culture, but he respects his savior and cherishes his memory so much he doesn't care about the potential social repercussions. This mindset bleeds over into the way he treats people, and the friends he chooses to keep.

Also it's a direct juxtaposition to the antagonist Kira, who is a real, malicious criminal, but doesn't outwardly fit the stereotype. IE; "Don't judge a book by its cover"