My biggest issues personally are the lock-in of systemd overall and for journald the binary file format. If I could use journald on its own with OpenRC first and foremost and preferably have it store logs as text be it json or whatever then I would use it hands down.
Journald just works for the most part and is much more convenient in most regards nowadays. If I remember correctly, interop was more of an issue before the big distros started to switch to systemd but now things seem to have mostly worked themselves out.
With regard to my comment about wanting logs stored as text, it really just comes down to having had to deal with corrupted binary files one too many times and unless it is absolutely unavoidable I find myself preferring text files for that reason. I'd imagine file system based compression leaves most if any storage benefit from binary logs rendered moot.
I know you can run a secondary syslog daemon from the output of journald or alternatively use a job to backup to a text based format but it would be so much more convenient to be able to just set a config setting. Having easy config and things "just working" is supposed to be one of systemd's strengths anyway.
Final thing to note is that at least from the perspective of someone running Gentoo w/ OpenRC, issues with traditional loggers are typically config mistakes more than anything. As for your debian log example, syslog-ng which I believe Debian had used should default to isodate for the datetime format. At least this is the case after RFC 5424 was adopted in 2009. That should give something along the lines of "1985-04-12T19:20:50.52-04:00". Nowadays unless the defaults are changed, most logging systems shouldn't have that datetime issue.