I swear the exposure stacking looks worse than it used to. iPhone X and XS manage to merge exposures without looking like the subjects are stickers that are placed on the photo.
I think the main difference is that the previous versions of Smart HDR in the X, XS and 11 all took 1 or 2 exposures and merged them using light metering as the metric, i.e. if you took a photo that included a bright sky and a darker ground it would take 2 exposures and merge them where the sky meets the ground. However newer "Smart HDR" tries to make sure that people are exposed brightly, which means it stitches in brighter exposures for subjects of the photo, making the photo appear unnatural.