It's more like the opposite. journalctl -k displays the kernel messages, but with a considerable amount of extra overhead because it has to go though the journal daemon.
Not disputing your point, but some of that extra code does allow you to do cool things. Add a `-k -b=-{n}` to see a previous boot's dmesg, or filtering with `-k --until` for time filtering, &c. All with the same interface you're using to process your other logs too.
https://github.com/systemd/systemd/blob/9afd5740391980fee5d8... https://github.com/systemd/systemd/blob/9afd5740391980fee5d8...
Whereas dmesg reads the kernel messages directly from the kernel.
https://github.com/karelzak/util-linux/blob/99c92a4820569970...