@Flare77
rephrasing the events, to the point that I know the basic gist of what happened during her trip without actually reading it
just because there are flashbacks to previous arcs/events it doesn't make the the previous arcs/events pointless because there would be a weird continuity gap for readers. and as ilikepi31415 stated, for underlying themes and character development
All the development of her fighting the ancient sexism only resumes once she goes back to Flourence.
Arte and some other females characters fight sexism in many different ways in this manga, and sexism happened in some different ways during that arc, so by saying 'sexism only resumes' you are denying a
constant conflict in this manga
From the gist of how things went, the only very important bit is that she was good enough to draw the eye of a very influential family but declined it.
Based on the summary of events, that's correct, but based on the
details of the events (which you haven't read), a lot or readers (like me) would agree that is incorrect.
the jump of her skill level between before and after her leaving is fairly obvious
Yes, but that's not what I'm referring to when I describe 'Arte growth as a professional artist',
I am referring to Arte learning: differing opinions (both positive and neutral/slightly negative) about her art, how to interact with different nobles as a professional artist, some other duties of a professional, etc.
Also, the gender/social (class) disparity details the manga has shown us during that arc will likely be more relevant when Arte works for nobility again.