In general I agree with you about the ability to customize Linux, but the author could be referring to systemd, which (from what I've seen) has been the target

In general I agree with you about the ability to customize Linux, but the author could be referring to systemd, which (from what I've seen) has been the target of many complaints about being too central and hard to replace, especially with how it is required by so many projects in the Linux ecosystem (from distros like Debian and Arch to DEs like GNOME).