The main issue here is that Oda's symbolic formula when it comes to taking down villains, is to do it in a manner where it is showcased in front of the people they have been oppressing, to signify the rebirth of that Country. In Big Mom's case, that would be the people of her own Country, whom she charges a soul tax on.
Even if he mirrored Thriller Bark, and she gets defeated, and all the souls she's taken over the years end up going back to their original people, it still doesn't fit the bill, because on Thriller Bark, there was still a massive audience of people there to witness Moriah's defeat, who had their shadows taken.
So Big Mom being defeated on Wano doesn't make any sense. There is literally nobody there to witness their freedom coming to fruition first hand. That drastically reduces the emotional impact of the act of having the Big Mom taken down once and for all. Oda doesn't do that, because he likes the defeat of the main villain to have these huge emotional climaxes.
Elbaf itself would fit the bill, because Big Mom has had bad blood with the Giants for years. So it's well within the confines of the story that she has taken a couple hundred/thousands of years of souls from the Giants.
Most people want her defeated because they just want her out of the picture. But Oda needs to conclude her story in a satisfying manner no matter what. Will he reduce her down to a secondary antagonist and have her taken out in such a way that goes against how he concludes the character arc for every other major villain? I personally doubt it, but you never know.