I've a feeling this started as a failure to communicate (and understand). The fact that systemd spews a stupid amount of stuff into dmesg when debug mode is enabled is a bug and the root cause of the problem. But the bug report mentioned that only tangentially and suggested a solution which didn't address the root cause of the bug, which would be fixing the debug spew. The argument then focused on the whole 'kernel owns the command line' issue and completely failed to mention that the debug spew bug had already been fixed (in systemd, and there is some work to add rate-limiting to dmesg).