If the problems with sysvinit are all imaginary then why has every other UNIX replaced it?

Mac OS X has launchd for 10 years now.

Solaris 10 replaced sysvinit with SMF.

Don't have any experience with AIX but the documentation says it has a "System Resource Controller" with a "srcmstr" daemon to manage services; though it looks like it runs on top of something sysvinit-like:

http://www-01.ibm.com/support/knowledgecenter/ssw_aix_61/com...

BSDs have generally never used sysvinit, although they do have shell-based service management.

So actually none of the particular examples you cite use purely sysvinit to manage services.

And it's also quite obvious that there are use-cases where reliable and fast service management are very important on servers.

One is containers, where you may run 10000 of them on a single host, and you have to reboot the host some time too, so you don't want to delay the start up of all those containers by loads of slow and racy shell scripts. Or even better, you want to have socket activated containers that don't actually start until they are needed.

https://www.getpantheon.com/blog/pantheon-running-over-50000...

Another is hyperscale servers: There are now really small ARM and x86 based servers and you can put 4-500 of those in a single rack. That means a lot more individual servers to admin, and failure modes that are relatively rare in current server rooms will become an order of magnitude less rare, so more robust OS level service management is helpful.