The scenes that most people remember are Bart skateboarding naked and Homer having Spider-Pig, each of which happen before the main plot (Springfield having a dome put over it, due to being environmentally unsafe, and the Simpsons escape, due to the residents wanting to execute them after Homer caused it).
Back when the movie was released, it was amongst the highest-grossing movies, so its not like it was some niche movie.
I think that, if they were going to make a movie out of The Simpsons, they should have done it in the 90s, and they should have based it on the plot of Sideshow Bob's Last Gleaming.
It still has the "epic" stakes that you'd want in a feature-length movie. It brings up themes that The Simpsons was known for making jokes about in the show and turns them up to 11 (e.g. Sideshow Bob's culture war against the depravity of television; Clinton-era liberal imperialism; even the whole theme of "nuclear" stuff with Sideshow Bob and the nuclear bomb). It would still have been political, but without being tied to the era of An Inconvenient Truth and Al Gore the way the actual Simpsons movie was.
I also think it would have been better having Sideshow Bob as the villain, rather than introducing some new guy. Sideshow Bob is the perfect antithesis to everything The Simpsons stands for, and the movie would have aged better -- I mean, Sideshow Bob basically believes everything current-day reactionaries believe.
Your vision is beautiful c: