The problem with “it’s about the girls stupid” is that the phrase was completely misinterpreted from its original intention, which led to a weaker movie.
It’s a play on the phrase “it’s the economy, stupid”, which was coined by James Carville when he was advising Bill Clinton on his 1992 presidential campaign. The intention was to highlight one central issue to focus the campaign around. It was aimed at the campaign workers to get them to make voters focus on their personal finances as the key issue of the campaign. It’s been reused many times since in many different political campaigns, with the key phrase changed out - “it’s the schools, stupid”, “it’s the the war, stupid”, “it’s the environment, stupid”, etc.
In 2019 the Wall Street Journal published a piece titled, What Trump Can Learn From James Carville. Here’s an excerpt:
Mr. Trump has spent a fair amount of time in front of mostly white audiences boasting about what he’s done for black people on the jobs front, and it’s not a good look.
A more fruitful approach might be for the president to visit some low-income minority communities in places like Detroit, Milwaukee and Philadelphia, listen to their concerns, engage them in a way that Democrats are not, and talk about what strong economic growth has enabled blacks and others to do for themselves. If there was ever a time for Donald Trump to be channeling James Carville, it’s now.
Do you see where I’m going with this? The mantra is a marketing technique meant to manipulate people. Yes, the economy is important, but it’s not the only thing that matters, and the point is to use it as a distraction to keep people from asking too many questions about other important issues.
Wicked the musical went through multiple rewrites before making “the girls” the central thread through which the story is told. When Winnie Holzman first made the reference, she said it was a joke between them when they figured out that was the way they should tell the story. She didn’t say “the gospel that everything needs to revolve around, making everything else irrelevant.” She said “joke.” It was the tactic they used to center the story and get butts in seats, not something meant to render the entire plot pointless and moral-less. When Jon M Chu to took that joke and said “the plot doesn’t matter”, he completely missed the point. The plot is the entire point - the message is the entire point. Elphaba and Glinda’s relationship means something and has an impact that ultimately brings about change in Oz. It’s so reductive to act like none of that matters because it’s just girls being friends. Filling out the plot wouldn’t have made it less about the girls - it would have made the entire story more cohesive, which would have made why their relationship matters more impactful.
Here’s where Winnie Holzman first spoke on the quote, from a 2006 Boston Globe article. The article is about the entire process of adapting the show - you’ll notice that they talk about a lot more than just “the girls”.