will you also deny that strawberry panic ripped everything from marimite? the difference between yagakimi and strawberry panic is that yagakimi isn't a soap opera and is actually good (seriously, i tried to rewatch it a while back and couldn't get through even half of it).
Strawberry Panic was pretty much a methodical parody of Marimite, not a ripoff of it.
I still don't see much evidence for the overall thesis you're putting forth. The play in Yagakimi had a very specific function in the plot and in the dynamic of the characters. The movie here just seems to be the occasion for getting this group of characters together (and I can think of a half dozen other manga that have had some kind of play/movie/performance as the instrument for allowing the various characters to interact).
Honestly? Hajime's desire to make a movie reminds me more of Kumiko's growing antipathy towards music at the start of Euphonium and her eventual realization that, yes, she does in fact still love music and the euphonium. Yagakimi's play was never about the play but about Touko realizing that yes she deserves a life outside of pretending to be her sister. That she can have her own dreams and desires.
Hajime isn't making a movie for someone else, she making a movie to make a movie. Because she enjoys film. And while she was finally pushed over the edge because of a pretty girl, her love of film is something that is truly hers and not something that is given to her.
Honestly you could make a better argument for similarities between this manga and Revue Starlight.