To be fair, some of this is driven by real needs. People want fast boots, so you have to work tightly in parallel. That requires a clear and complex dependency

To be fair, some of this is driven by real needs. People want fast boots, so you have to work tightly in parallel. That requires a clear and complex dependency graph. That requires significantly more than some symlinks in /etc/rc?.d/. Also as distros aim to pare down their default installs, you end up in a situation where there is very little that you actually can disable without breaking your ability to boot. Furthermore, given typical CPU/RAM overheads on modern hardware, disabling something that takes a fraction of a second to start and consumes almost no RAM can seem slightly pointless! I'm not familiar with systemd, but upstart takes a similar approach to sysvinit - don't want something to start? Just move it out of /etc/init/ like you would have rm'd the symlink in /etc/rc?.d/ :)