> to embedded systems where boot time is critical.

if it's critical on an embedded system then you're not running systemd at all

> The number of systems that have 5 minute POST times and need deterministic boot is an edge case of an edge case.

desktop machines are the edge case, there's a LOT more servers running Linux than people using Linux desktops

> Relying on emergent behavior for consistent boot order is bad design.

tell that to the distro authors who 10 years in can't tell the difference between network-online.target, network-pre.target, network.target

And a very large number of those Linux servers are running Linux VMs, which don't POST, use systemd, and have their boot time dominated by the guest OS. Those servers are probably hosting dozens of VMs too. Boot time makes a lot of difference here.