Thank you for the response, Damien. I'm not quite clear on what you mean by "pick a style to use, then you resize it to fit", where can the user pick a style from?
In looking at this from a user perspective, as far as I can tell the user is presented with an interface where they select the image and are given drag handles to resize to seemingly 'infinite' size. If they expand the dimensions beyond the max style width, which is not something displayed to them, the image editor shows the image expanding as expected, however upon saving the rendered page ends up adjusting the size to the "default" style width. They then either assume the resize did not work at all or they need to play a bit of a guessing game saving in smaller sizes until they find one that is below the unknown-to-them max.
I'm not sure on the technical difficulties in doing so, but in my head in an ideal world the largest available style would be rendered.
I suppose a workaround might be for us to set the Default style to our widest one, but that feels like it will more often than not be an inappropriate default selection.