Broly's story is garbage, first off. How much can you remember of your early years as an infant? How likely do you think it is that you could remember something from THE FUCKING DAY YOU WERE BORN? And that's the thing that kills Broly's entire character from day one. His ENTIRE MOTIVATION FOR EXISTING is because Goku, who he did not see, who he COULD NOT POSSIBLY SEE IN THE POD NEXT TO HIM, was crying too loud.
Second, his entire design subverts the entire theme of the franchise. Every time there's a big beefy monsterguy, he always loses to the smaller, leaner hero. Or, if there's a big, beefy transformation, it's inferior, like Super Truns, Cell beefing himself up, or Frieza's transformations. Broly bucks that entire trend by being this big stupid Meatman who jut destroys everyone and has no weaknesses.
THIRDLY, he just reads like bad fucking fanfiction. "Oh, no, this guy's the TRUE Legendary Super Saiyan! Every other Super Saiyan ever? They're not real, they're just shitty knockoffs. Broly's the REAL one! Look how cool he is! He was stronger than Vegeta when he landed on Earth AS A BABY! He blew up planets as a toddler! He's CRAAAAZY! He walks right through the Kamehameha!"
And it's not even like the Frieza saga, where there was this huge mystique surrounding Frieza, about how terribly powerful he was, and then Frieza actually starts fighting and backs it up, and nothing, absolutely fucking nothing works. That's real peril, because our heroes have been making headway in their goals, and they're succeeding, and Goku's here, and Piccolo's back! They can do it! But they can't. Piccolo gets a hope spot, Vegeta gets a hope spot, even Goku gets a hope spot, but they can't do shit. There's drama and there's tension, because there's stakes, and there's moments where you believe our heroes can actually turn the tide, but it accomplishes sweet fuck all. Here? "Oh, Hey, Goku, it's King Kai. There's this random asshole that's superstronger than you could ever be." And there's no tension, because nothing changes, Broly just walks through every single fucking attack in the movie, LITERALLY walks through it, and only dies at the end because the runtime says the movie has to be over and the heroes have to win.
He's just garbage. Everything about him.