Xbox One X has 75 second load times for fast travel, cut back features to match base Xbox One along with already not having smart delivery. Guess I'll pick this up in a year or two on sale for next-gen.
I would guess that the Xbox One X wasn't a high priority due to not representing much in the way of install base, hence why it doesn't seem to have gotten much fine grained tailoring. Still, at least they didn't skimp on resolution, unlike some releases where it's a match for the weaker PS4 Pro. 1080p to 1440p is around a doubling of pixel count.
I still feel like the last gen version as a whole represents a decent effort overall; performance isn't perfect even on Xbox Series X, so getting it running acceptably on last gen can't have been an easy task.