Yes, true. Ehh, well, no actually
Dates by themselves are rather easy and specific. And they are plain numbers, so what more could a maintainer of a database wish for?
The issue here is more about deciding which dates are relevant to store and how to give them a place and availabilty so that humans can make use of them.
To this human, it is relevant to see in what year (when/if) a song was released as a single.
And I also want to easily see that if the song happens to be on some compilation album, and not only if it is on the original single/album release.
The same for original albums in a box-set.
Sure, MusicBrainz is doing nothing wrong technically when it fills the ‘original year’ with the first year that that box-set was released.
But this human is also (read: more) interested to see the original release years of the albums that that box-set contains.
Of course, any of this information can be looked-up, and in some cases it may be a somewhat subjective matter.
But in principle I feel it would be very logical (in a human way) to have such dates available.
Pretty much any music lover will have songs or albums matched to ‘original’ dates in their heads in some way of another.
It would be nice to have MusicBrainz/Picard understand—and accommodate for—that.