Twice may not be AS popular as in 2016-2018, but that doesn't make them flops. and that doesn't take away their impact. They were given the name of the nation's girl group, a title they still currently hold. As well as lead the third Hallyu wave. They are incredibly respected in both nations and to top it off, they aren't done growing. Every comeback they're gaining achievements in the west.
Every group has a peak and every group declines in their later years as trends change and new groups emerge, but that doesn't take away their impact.