PGP _supports_ up-to-date, secure cryptographic algorithms, but it's usability falls short. these new algorithms are rarely made the PGP implementation's default algorithms.

Those algorithms are unsuitable for messaging as implemented in gpg.

Because the usability sucks (supposedly leading you to shoot yourself in the foot), not because of any problems with the crypto or the implementation.

The crypto is also very questionable for any use case relevant to briar.