Please elaborate here what "inadequate" exactly means, and what "insecure defaults" mean, and which version this refers to.

inadequate:
gcr-prompter prompts me for my GPG passphrase. I never configured it to do so, so I start looking for its documentation and do not find any at all in the gcr package.

insecure defaults:
Caching a GPG passphrase for the whole session by default is not good security practice.

version:
gcr package  3.10.1-1  as shipped with Ubuntu 14.04

gcr-prompter is not in the $PATH anyway so I have doubts that creating a man page would be a useful effort. (I'm not a gnome-keyring dev though to judge.)

> Caching a GPG passphrase for the whole session by default is not good
> security practice.

Who defines a "good security practice" here and with which arguments?

Well, even a README would help that explains what the package is about which could then reference further documentation to help users understand where the appropriate configuration can be found.

I doubt you will find any security professional who would call caching a GPG passphrase for the entire session by default. Especially when it is not obvious where and how this behavior can be changed.

gnome-keyring no longer implements a gpg-agent. The gnupg agent and pinentry have been better integrated with GNOME.

https://mail.gnome.org/archives/distributor-list/2015-August/msg00000.html