Admiral Noble ( aka bad guy with the ridiculous bowl haircut and tentacle girlfriend) commands a flagship that is carrying multiple high value prisoners. ( General Titus, Tarak the quasi Bravestarr guy, the Bloodaxe siblings, Nemesis the sword lady and Jimmy the thoughtful robot) He's bringing them to his leader because one of them, no one knows which one, has the location of Kora. She's either the sister or daughter of Motherworld leader Balisarius. He needs her because he's dying and her organs are the only ones that will work to save his life. She ran after he killed their adoptive father, the former King of Motherworld ( the Princess Bride guy)
Kora pays Jax Teller Solo, a ruffian high level black market pilot, to fly her to intercept the flagship and break out the prisoners, that way the person who knows her location, plus the location of her "resistance" won't be able to talk/be tortured for the information. During the breakout, everything goes wrong, chaos happens, lots of people die, and the flagship crashes on a nondescript planet. It splits in half. Noble and his survivors are enough of a fighting force to overrun Kora and the prisoners, whose half of the ship crashes near the farming village.
Jax Teller Solo's ship is badly damaged in the fight in space and is still in space. Needs lots of repairs to fix it well enough to drop inside the planet to rescue Kora and escape before Motherworld military reinforcements arrive. Kora cuts a deal with the prisoners. Fight with her and defend the village long enough for the USS Sons Of Anarchy Falcon can come to rescue them. And get a ride off the planet and escape before a large portion of the Motherworld fleet shows up and kills them all. Kora points out that they are only still alive now because no one knew for sure which one knew her real location. Now that she's 'found', these prisoners have no more value and are ripe for immediate execution. And they owe the villagers, who saved their lives from the crash.
In the process of defending the village, we get to know the prisoners and their backstories. We get to understand their skills, weaknesses and their problems with each other. Head farmer Gunnar and the village Mayor in Billionaire Mike Prince from The Strain argue about the best strategy. Baldy wants to surrender the prisoners and village and be spared, it's not their fight. Head farmer has the hots for Kora and thinks otherwise.
Three major battles. The first in space that opens the film. Just straight up carnage and death. Lots of spectacle and fury. Second battle is a smaller Motherworld force being repelled to defend the village. These are the Motherworld troops who survived the crash on the back half of the ship with the prisoners. This fight allows us to see the skills of the individual prisoners/fighters. The third fight is the major one at the end with Kora and her new Magnificent Seven plus the villagers against Bowl Cut evil guy and his much larger force.
You can have the same sidebar beats - Nemesis being a tortured ex mother who lost her kids and fights a spider woman ( used to torture prisoners) . Bravestarr being an animal whisperer. The Bloodaxe brother dying at the end. His reluctant sister now is invested in the future fight. Jimmy's search for understanding humans with the relatively hot farm girl. Jax Teller Solo being a traitor ( He was trying to "deliver" Kora to the Motherworld) . You can add some scenes early in the film where Noble is torturing and killing people to find more information about Kora's location. This allows pure exposition to talk about the prisoners, one by one, on their backgrounds and their threat to the Motherworld ( with immediate flashback montages highlighting their skill)
Leaves plenty of room for a Part 2. The new "Seven" escape, but for how long. Now they are stuck together. They realize their chances to live are better together than alone. But maybe make head farmer Gunnar less of a total simp. And in Part 2, you can cover more about Kora being trained as a soldier, falling in love with a fellow soldier who got killed, being "used" to indirectly cause the assassination of the King, etc, etc. Last scene is Noble sending a video feed to Kora. While she escaped, she broke her promise to the villagers to take them with her and her new crew. She had to leave without them to save herself. Then Noble kills them all in front of her on video. Farm girl and her new boy band former soldier boyfriend watch in horror as her entire family is massacred. They made it to the ship with Gunnar, but no other villagers.
And you can still have a scene where Corey Stoll gets his head caved in, which should please the general audience plenty. The after credits scene shows that one of the "prisoners" is a Motherworld plant. They are a notorious "criminal" in that universe, but they were always controlled opposition by the Motherworld to help smoke out Kora. A presentation to lull any resistance into slipping up and revealing themselves. Who is the real traitor among them now?
Fifteen minutes. Fixed. Nothing ground breaking. But better fights, more efficient exposition, better set up for future films, better incentive for everyone to fight the Motherworld, better motives for Kora's value and her pathology, better pathway to show the Motherworld as something other than mustache twirling cutout villains ( You fail and you die in this universe, they might not want to kill the villagers, but it's these peasant strangers or their own lives instead, not much of a choice)