Over on https://bugs.debian.org/799631, Elliott Mitchell writes:

While this system has this older revision of GPG2, examining later
versions seems to indicate this issue is present there too. When
exporting data, one may well want to export *only* one signature
(their's) for a given key. For instance, this is useful when confirming
an e-mail address is associated with a given key by sending the signature
to the e-mail address. In such a case it isn't necessary to send copies
of any other well known signatures, only the one new signature.

I'm pretty sure this is upstream and also effects gnupg v1, but is very
much an issue for v2.

This seems like a feature request for a new value for export-options, something
like:

  gpg --export-options export-only-certs-from=$MY_FPR --export $THEIR_FPR

This would be like export-minimal plus the most up-to-date certifications on the
given user ID from the key identified by $MY_FPR.