The journal still takes over /proc/kmsg. You're relying on journald working properly, and you cannot bypass it. Forwarding things on from journald is not the same as disabling it completely.

(This sort of inability to make decisions about what tools you use for your system is one of the complaints about systemd)

That's not disabling journald, that's disabling journald writing messages. It's still receiving every byte sent to the system log, it's still in memory, and otherwise still running.