The Buu arc of Dragonball Z is generally agreed to be the weakest of the bunch. The arc contains several beloved plot beats, like the relationship between Mr Satan and Fat Buu and Vegeta’s excellent character arc, and also contains many interesting concepts like fusion, Gohan’s relationship with Videl, and even Majin Buu himself. Unfortunately, it doesn’t gel together at all. Many of the most interesting additions to the story are totally extraneous, and the relentless focus on the rivalry between Goku and Vegeta undermines the conclusion of the Android/Cell arc where Gohan is supposed to be taking up the mantle of Earth’s defender from Goku, who is falling behind the rising power of his son. That passing of the torch lasted all of one fight before Goku shows up, having far exceeded Gohan once more.
Arthuriana thrived on its ability to discard or rewrite bad stories while keeping good ones word for word. I think losing this ability, in part because of copyright and in part because cinema means that cutting together films shot in different eras makes the seams extremely obvious, makes modern storytelling weaker. Given a chance to reboot Dragonball Z, I’d make only minor edits to the Saiyan/Freeza arc, and while I’d revise the early Android/Cell arc (the androids themselves are wasted as villains), I’d want the conclusion to be mostly a shot-for-shot recreation. For the Buu arc, however, I’d go with a total reconstruction with the goal of salvaging the good bits while reframing the context such that they actually matter. In the existing Buu arc, all fusions and every action taken by both Gohan and Mr Satan could both be completely excised and it would change nothing about the ultimate conclusion.
Given the opportunity to rewrite the arc, I’d implement what I call the Three Buu Solution: Having not one, but three pink demon genies, each of Buu’s three different forms being different characters altogether, who appear right alongside one another. This allows for three coterminous plots that can emphasize three different sets of characters without reducing some of them to a sideshow in which a heroic effort is made to defeat Buu and it just doesn’t work, so everyone ultimately may as well have just waited for Goku to do it. Again.
One of the three Buus, probably Kid Buu, is ultimately just a proxy for the rivalry plot between Goku and Vegeta, and involves Majin Vegeta playing for the bad guys until the very end when he has his moment and explodes himself to defeat Buu. This is easily the most compelling character arc of the Buu arc that we actually got, so the only major change I’d make is that Vegeta’s sacrifice actually does eliminate one of the Buus. I’d consider excising Goku from this plot completely and instead letting Gohan take his place. The arc is really about Vegeta, and while Goku has been his traditional rival, that was only in part because of their personal history. Gohan has surpassed Goku in power, which means Gohan is now the one to beat. On the other hand, Vegeta does have a lot of personal history with Goku, and having Goku play this role helps build up Vegeta’s story, which is supposed to be the focus of this part of the arc, so I lean towards using the “Goku is brought back temporarily” device.
Gotenks iconically fought with Super Buu, but I’d have him fighting Majin Buu instead. This arc also requires a revision to the Babidi/Debora sub-arc, to make Goten and Trunks less cooperative. Having them team up to sneak into the adult competition was kind of funny but is not really a beloved moment for anyone, and it makes their fusion significantly less of an accomplishment. It instead mainly serves as a setup for Goku and Vegeta’s fusion later on, which doesn’t even accomplish anything, and is thematically exclusive to Vegeta’s sacrifice. Vegeta’s arc can conclude by putting aside his rivalry to team up with Goku, or by putting aside his rivalry to ignore Goku and fight Buu instead, but doing one after the other is redundant. I like the second one because it places the emphasis on what Vegeta cares about more than beating Goku, but you can make an argument for the first one.
Another advantage of having Vegeta complete his arc with his sacrificial big bang attack is that it allows Goten and Trunks to be the stars of their own fusion arc, having a more strained relationship from having inherited their fathers’ rivalry. You could even do a thing where Trunks tries to join Babidi to follow his father, which could prompt Vegeta’s final heel-face turn, and whose subsequent sacrifice can serve as inciting incident for Trunks and Goten’s arc culminating in their fusion to defeat another of the Buus. I favor Majin mainly because the childlike terror serves as a good foil for two child heroes.
That leaves Gohan to fight Super Buu. Gohan doesn’t have the relentless dedication to training that Goku did, and after seven years of peace, he’s been slacking off. In his early fights, he does poorly. Despite the power of his super saiyan 2 transformation, he loses a fight with Vegeta (either a tournament bout or an early fight with Majin Vegeta), leaving Vegeta dissatisfied with Gohan as a substitute challenge for Goku, and when Super Buu first emerges with the other two, Gohan is immediately crushed by the most powerful of the three. Piccolo, Krillin, Tien, Chaotzu, Yamcha, Videl, and Eighteen team up to try and defeat Super Buu, or at least hold him in check, while a badly injured Gohan retreats to the Supreme Kai, who offers him special training (not just some kind of mystic power transference, but actual training in some kind of hyperbolic time chamber, or else something that’s intended to remove a specific mental block in time to defeat Super Buu).
The plan of flinging all the weakest fighters at Super Buu to buy time while Goku and Gotenks wrap up their own Buu fights seems like a good one at first, because after winning, Goku and Gotenks can use senzu beans to immediately restore their health and fight Super Buu together. Super Buu’s absorption abilities throw a monkey wrench in that, and with Goku already fighting Majin Vegeta and Kid Buu and Gotenks already fighting Majin Buu, the remaining Z warriors have only two choices: leave Super Buu to wreak havoc upon the Earth unopposed, or fight to stall him and try really hard not to get absorbed. They go with the second one, and it doesn’t work out great for them.
Vegeta sacrificed himself to defeat Kid Buu, which means Goku and Gotenks are the only ones left to try the team-up against Super Buu, but everyone except Piccolo has already been absorbed, which has left Super Buu with a huge array of techniques in addition to the incredible strength and resilience he started with. Piccolo backs off to pop a senzu and recover, since continuing to fight would only risk him being absorbed, and Goku and Gotenks go at Super Buu together, but to no avail. Gotenks gets beaten out of the transformation and back into Goten and Trunks, who are absorbed, and Goku follows soon after. Piccolo prepares for a doomed last stand against Super Buu, but Gohan saves him at the last second. Gohan is able to fight Super Buu to a standstill at first, but he’s tiring rapidly while Super Buu never seems to run out of energy. Realizing that Super Buu is drawing on the energy of all the people he’s absorbed and that this must mean they’re still alive (there’s an upper limit on Super Buu’s own ki reserves that prevents him from just sucking ki out of the Z warriors like a vampire or something, so he must be using living Z warriors as ki batteries), Gohan allows himself to be absorbed in order to fight his way out from the inside, saving the other Z warriors in the process. Reduced back to his original power, Gohan is able to defeat Super Buu and save the world.
I like this solution for a number of reasons. First, the triumvirate of villains breaks the pattern set by King Piccolo, Freeza, and Cell, which was becoming formulaic (Cell’s efforts to absorb the androids helped keep things fresh, and this arc likewise has one of the three Buus be noticeably stronger than the others, allowing for a climactic confrontation with the strongest of the villains, but still breaks from the King Piccolo/Freeza formula of a single ultra-powerful villain in enough ways to keep things interesting). Second, by splitting the bad guys up into three different villains who must each be overcome, it is much easier to make all the wide variety of good character moments actually important to the overall arc, rather than being reduced to so much sound and fury that ultimately accomplish nothing. Third, it allows Gohan to be Earth’s protector in the end, thus building on the conclusion of the Cell arc rather than reversing it.
I still wasn’t able to find a place to get Mr Satan’s arc in there, but I’m sure you could find a place for it somewhere, particularly since it could serve as a good B-plot to stall Majin Buu while the A-plot focuses on Majin Vegeta, Goku, and Kid Buu. The main thing is figuring out how to handle the conclusion.