I had that same hypothesis as well until recently when I disabled some unnecessary daemons by 1. booting into Recovery with SIP disabled and 2. changing a handful of the /System/LaunchAgents/*.plist files to .plist.bak files, effectively disabling for all future reboots.
Since doing this, I've gone through a few security updates and was expecting the udpates to find that the original .plist files were missing and put them back in, but alas they did not as they remained as is.
Since doing this, I've gone through a few security updates and was expecting the udpates to find that the original .plist files were missing and put them back in, but alas they did not as they remained as is.