Launchd 2.0 changed the syntax for the launchctl commands (and made it closed source as it now heavily relies on XPC.Framework). The man page for launchctl lays it all out. Load and unload became "bootstrap" and "bootout". Start became kickstart. As far as I can remember enable/disable are still the verbs, though in order to see the status of jobs' "enablement" you have to use the poorly named "print-disabled". Though the latter only matters for jobs that can actually be disabled, ie, any that have the "Disabled" key set to true in their plist file. By default, jobs in the various LaunchAgents or LaunchDaemons directories are always enabled and always loaded at login or boot respectively.

I literally teach people how to use launchctl every other week. I've found it's unituitive for learners because init systems tend to be unintuitive because there is a lot of hidden action and state going on. It wasn't until I started using it on my own I could develop some instinct for it. Personally, I don't find launchd anything but more ergonomic than systemd. A few man pages and some experimentation and you're at least crawling.

Not to say it couldn't be improved; I'd love to know why a failed bootstrap can't call plutil to at least lint the goddamn plist to notify of basic formatting issues instead of printing the same useless error for everything under the sun. "Error 5: Input/Output error" might as well just be an exit status of 5 for all the help it gives me.