I'm not familiar with this as an option.
However the documentation -Set image upload options - does state: You can also define the image display sizes when embedding images in posts.
I don't see this described in the table on the page though. 🤔Unless it's referring to setting max width.
I've just checked in with our engineering team and at this moment in time, there's no config to be able to define which size is the default.
I would recommend posting this on our ideas exchange for the product team to investigate if it's feasible and if they take this on, where they can add it on the roadmap.