It lacks a hybrid duration type. Instead, it splits durations into calendar and time durations and conflates the length of a `day` depending on whether it's in `Period` or `Duration`. And AFAIK, it doesn't support time zone aware duration rounding. And I don't see a way to compute a `Period` from two `ZonedDateTime` values in a way that respects time zone transitions.

To be clear, it's good. But there are mistakes that the Temporal project learned from and fixed.

(Temporal's single `Duration` type does have pros and cons, so I don't mean to frame having two distinct types as a strict negative. But it's very clunky.)