> You can also argue that sd_journal (the C API) exists for this exact reason, rather than shelling out to journalctl.

Quoting from https://systemd.io/JOURNAL_FILE_FORMAT/

> If you need access to the raw journal data in serialized stream form without C API our recommendation is to make use of the Journal Export Format, which you can get via journalctl -o export or via systemd-journal-gatewayd.

Certainly sounds like running journalctl, or using the gateway, is a supported option.