I would just add to the comments here by saying that, as a publication owner, we're now dealing with hundreds of "broken" stories. We historically used a full screen width header image for our stories - it was part of our brand identity.

Because the changes around image sizes are retrospective, we now have a large body of work ahead of us to fix our historical stories. Given the volume, we might have to settle with spot-check fixes.

I understand and support the need to make navigation easier and more intuitive. And I'm sure there's user research pointing to the value of making these changes. But the road is becoming increasingly tough for publications on Medium, and I think this change only adds some nails to the bitumen.

In terms of a way forward, I'd love to see some of these changes (especially around images) being an option publications could toggle on and off (at least until we sort out our styling).