Don't hard links suffer from the issue that because they're actually links to a specific file, not path pointers, that you can replace the target file thinking you have updated something in the system and instead have stale hard links lying around, referencing the older version when you intended to replace the older version for all users?
I think that in a hypothetical world where symlinks worked like hard links, we'd be swapping out the security complaints in this post for articles about how hard it is to upgrade a POSIX system properly, tools and tricks you can use to make sure you truly replaced all instances of a binary with a known vulnerability, and so on.
What I mean is that it's pretty SOP to have a package that installs a new command to work by installing to /opt/my-package and then symlinking /usr/bin/my-cmd to /opt/my-package/my-cmd.
In the absence of symlinks, that link would be hard and dpkg et. al would have to do package management by deleting the /usr/bin/my-cmd link and re-creating it instead of letting it ride, trusting that it will point to the correct thing when the update completes because the target bin will have changed.
I think that in a hypothetical world where symlinks worked like hard links, we'd be swapping out the security complaints in this post for articles about how hard it is to upgrade a POSIX system properly, tools and tricks you can use to make sure you truly replaced all instances of a binary with a known vulnerability, and so on.