And somehow, I doubt that even the most fervent of fiddlers really enjoy typing obscure command line incantations just to configure their laptop when they connect it to a projector.
What you are thinking of is an API, not a command line interface. That still exists, and it can be used to build a command line interface. Command line interfaces by themselves are actually very poor for automation and integration, as they force you to do lots of unnecessary formatting and parsing in and out of text strings at every step.
For graphical tasks such as this, the command line is indeed obsolete. The main usage for remaining with the command line in modern times is for manual administration of a remote server, but that is not relevant here as the whole problem space is about administering the local machine as a GUI.
Anyway, xrandr is already there and Google and stackoverflow are full of examples. I'm not surprised that people would invest half an hour copy pasting code from there instead of identifying and learning the underlying API. I don't see why that should be a problem.
It is not true that command-line interfaces are not used to remotely administer GUI desktops. This is actually a huge and very common problem space.
See my other comment about impedance mismatch for an explanation of the challenges with using command lines to remotely administer GUI desktops. It can be something that complements GUI administration, but can never possibly supplant it, because if you do that then you're intentionally trying to route around the problem space.
> It can be something that complements GUI administration, but can never possibly supplant it,
There are probably tens of thousands of people whose daily lived experience is that command-line administration of GUI desktops is all they've ever needed and yes, in fact, totally supplants the alternative. I am really struggling with this thread; it's my impression that you've a very narrow view of what people are doing with their computers.