Not even sure what the point of it was other than to include Miku
I think the point is individuality as each wants to be recognized as their own person instead of being just one of the quintuplets, Miku didnt even wanted to be recognized differently until she found out he cannot tell then apart if they dress the same but her motivation was more about trying to advance the relationship instead of waiting.
There was also other stuff going on, besides why Miku did that with Itsuki also deciding to step up instead of being the "good sister and share", I think at this point all of then have their own arcs except Itsuki that have bits here and there but even Yotsuba had her own arc. I think it was well rounded as given a lot over most of the cast even if Yotsuba and Itsuki were not about romantic overtures.
I mean, its not easy to juggle 6 characters and this arc did given light to all of then.