Vim is running as you, rather than root, so you wont be able to edit other files as root, and any rogue plugins wont be able to either, which is good.
Sudoedit has various guards around what it'll let you edit, in particular, you can't edit a file in a directory you already have write permission on as doing so allows the user to bypass restrictions in the sudoers setup (there's more detail in their issue tracker. If the directory is already writable though, you don't need sudoedit anyway.
SystemD is far too much of a poorly thought through mess to have anything like a sane GUI configuration, it doesn't even have a sane textfile based configuration. We're going to have to wait fir SystemD to crumble under it's own weight and be replaced with multiple, simple, cleanly designed components before we have any hope of a sane config again. Sort of like we used to have before a certain someone/some company (depending on how conspiratorial you're feeling) decided to come along and muck it all up.
/rant
Thank you for coming to my Ted ~~Talk~~ Rant. You may gather I dislike SystemD quite a lot.