If Big Mom as a villain in the plot lasts all the way until Elbaf, then it's going to be dragged. Whole Cake Island and Wano is plenty.
We are nearing the end game. After the war, in my opinion it will be about Shanks, revolutionaries, Celestial Dragons, Elbaf lore, BB, Imu etc.
Big Mom should go down this arc by the new generation's other two leads, Kid and Law. Symbolically makes more sense after all this buildup of years of setup.
Luffy needs peers in some form. Not necessarily equal portrayal from Kid and Law, but comparable individual achievements.