> If it’s only happening under systemd, then I’d argue it’s systemd’s fault.

Yep. For me, it's most often a 90 second delay that comes from the combination of the automagical conversion of fstab entries into services, an NFS mount in fstab, and an offline NFS server.

Sane init systems notice that this is a networked filesystem (I've even marked it with the _netdev option!) and don't hang the boot for a minute and a half screaming at a dead server. Systemd is anything but sane.