Again, to be clear, I'm not saying it's impossible to do. But in order to do it, you have to build your own abstractions. And even then, you still can't do it because tzfile doesn't give you enough to do it. And tzfile has a platform specific API with no caching, so every time you parse a datetime with a tz ID in it, it's completely reloading the TZif data from disk.

Some of these things are implementation quality issues that can be fixed. Others are library design problems where you can achieve your objective by building your own abstractions. Like do you really not see this as something that shouldn't be mentioned in a comparison between these crates? You must recognize the difference between what you're doing and just plopping a Zoned in your struct, deriving Serialize and Deserialize, and then just letting the library do the right thing for you. And that mentioning this is appropriate in the context of the "facts of comparison" because it translates into a real user experience difference for callers.