Perhaps going from a full-frame sensor Sony a7R II camera to an APS-C sensor Fujifilm XT-5 would indeed be a downgrade. You can’t beat laws of physics, right? Given the same situation, the larger sensor Sony will always capture more light, with better resolving power, than the Fuji. I don’t suppose it’s typical that a photographer goes back down a step in terms of sensor size. Once they get to full-frame, they either stay there, or wait enough years to pay up for an ever larger medium-format camera.
I have my reasons for going back to an APS-C sensor, of course. As someone who is wholly satisfied with the pictures my iPhone outputs, I am not concerned about sensor size. A photograph is capable of telling a story no matter the tool that it was taken with. Physical limitations are something work around, rather than lament the lack of. The iPhone can never match the bokeh of a proper DSLR/portrait lens combo, but I can still be creative in how I frame the subject. It’s a sort of creatively that breeds from limitations.
The modern full-frame camera is simply too good. Most units from a major manufacturer can output pin-sharp photos in crazy high resolutions. There’s so much dynamic range, so much leeway to edit a file that the capture process almost seems secondary. Why care about getting the proper exposure or framing something just right when it can all be fixed in post-processing? And because you can get a photo to be even more perfect in post, editing becomes a necessary chore. You have to, because you can.
The reason I bought the Fujifilm XT-5 is because I only want to shoot. To use the JPEG images straight out of the camera (got to love those Fuji film simulations) - because I’ve already put enough thought to exposure and composition at the moment of capture. The point is to shoot more, and not spend hours in front of the computer editing. I am perfectly happy to give up some fidelity in pursuit of this. (Near) perfection is overrated anyways. A picture with blown highlights and or crushed shadows can tell a story just the same as one with the utmost amount of dynamic range.
Limitations breeding creativity.
Red is where the fun begins.