All of Spider-Man’s origin is told/alluded to off-screen. And the history of the Black Panther is literally told in an exposition dump at the beginning of the movie. Additional dialogue, acting, etc. flesh the story out throughout the film and enhance the characters’ motivations & arcs—I think that’s all I’m proposing for the FF.
Again, they weren't origin stories in the literal sense of the word, but they were still
becoming stories.
Spider-Man starts his film from an unfulfilled place. He hasn't met his first villain yet, hasn't had his first relationship yet, he hasn't even learned the true meaning of responsibility yet. But he does, over the film, acquire all those things, and learn what being a hero truly means, and what his purpose in the MCU, is.
Black Panther tells the history of Wakanda through exposition because it's necessary for us as the audience, to know this history, to understand the events that are about to play out in live narrative. T'Challa's arc of coming of age into a king, Wakanda's arc of change, Okoye's arc of foregoing tradition, Killmonger's rise & fall that challenges the status quo and T'Challa's beliefs-- are not relegated to exposition.
This is all formative stuff in the context of the Black Panther franchise.
The formation of the FF I don’t think is that appealing—we didn’t spend time watching Mr. Incredible and Elastigirl meet and form their love, etc. Nope, we want to see them as a superhero family upfront. I’d say the same is true for the FF too.
Well, that's because the film isn't specifically about Mr. Incredible and Elastigirl as a romance. If it was, we would have absolutely seen those moments. No, it's about them as parents and about the family. And the film does not begin with this family already formed as a superhero team. The formation and development of the family ("Incredibles") into a superhero team, is the live narrative of the film. So narratively, the Fantastic Four equivalent of this, would be the same.
I don’t want a Ben Grimm that’s still stunned by his rockiness; let organic moments in the script bring highlight his lingering insecurities in a smart way. And I don’t need a movie of Reed figuring out his place as a leader. Those just seem like retreads. Let’s skip that and get to the meat.
Then what is Grimm's arc? If not him overcoming his insecurities, and accepting himself, ane his body, what would be the internal flaw that he must overcome? What would he learn in this film?
Even the Incredible Hulk which takes place 4 years after the accident, still bolsters a Banner who has yet to come to terms with his condition. Because that absolutely is Banner's formative arc: acceptance