I might be missing something, I read both articles and do not understand the issue with 3 options. People interact with the theme change maybe once a year or so, a tiny amount of friction in that case is a non issue if that makes it simpler for the user to actually set the theme value they want (system default, light, dark). It really feels that they started with the idea that it should be 2 options, then try to come up with an argument
Their argument is that the user almost always experiences the moment of interaction with the controls as a single decision with 2 branches, (a) the OS behavior matches my expectations and I won't change it, and (b) the OS behavior violates my expectations and I want it to be the other one.
I'd also rather just select from the full tristate diagram, but their framing also makes sense to me