I get OPs point though - coming from an outsiders perspective I would have thought that a key feature of a time format would be to know how much time there is between two other times.
The standard for communicating time between humans lacks this feature for times more than a year in the future. That computers (which interface with humans) implement this standard faithfully is a feature, not a bug.
I agree it should be implemented but it could be implemented differently. Just like zoned datetimes are represented as a UTC time + timezone. UTC could be represented as TAI timestamp + leap seconds.