Would doing something like this work around the "journald drops the most important error messages" issue that has been known/outstanding for ten years (bug moved to GitHub six years ago), or is that more of a fundamental design mistake in systemd itself?
It's not accurate to say it "drops" error messages. The bug causes these messages to not be attributed to a particular unit - you can still see them with `journalctl` but not with `journalctl -u foo`. Still pretty annoying and should absolutely be fixed (although I'm not sure if systemd is the right place to do it).
> although I'm not sure if systemd is the right place to do it
It's truly impressive how systemd turns out the be the right place to do absolutely anything and everything from bootloader to init to dhcp to ntp to network shares... except fix systemd bugs. systemd doesn't seem to be the right place to do that ever. Someone else needs to do it. For another example of this phenomenon, see the nohup bug.