honestly in my experience it rarely matters (if you care about stable APIs) as most types you want to have at an API boundary are written (or auto generated) by you

this leaves a few often small types like `DateTime<Utc>`, which you can handle with serde serialization function overwrite attributes or automatic conversions not even needing new types (through some of this attributes could be better designed)

serde is not perfect but pretty decent, but IMHO the proc macros it provides need some love/a v2 rewrite, which would only affect impl. code gen and as such is fully backward compatible, can be mixed with old code and can be from a different author (i.e. it doesn't have the problem)

Anyway that doesn't make the problem go away, just serialization/serde is both the best and worst example. (Best as it's extremely wide spread, "good enough" but not perfect, which is poison for ecosystem evolution, worst as serialization is enough of a special case to make it's best solution be potentially unusable to solve the generic problem (e.g. reflections)).