First of all thank you very much for this indepth answer!
I just did a quick test to understand what you were saying. I tried to focus on a subject way too close for my camera and in release priority it took a picture and in focus priority it didn't.
So it seems it is not a fault of the software but rather wrong expectaions on my side.
Althhough I have to say that it still feels like a strange behavior of the camera. I for example have the focus lever on manual and at the same time have the back button set to continious auto focus with a single point (.i.e. having the advantage of manual focus and auto focus at the same time). The shooting mode is set to CL.
When I just tip the backbutton and then press immediately the shutter, no picture is taken. Therefore the camera feels extremely laggy.
Is this behavior normal and still falls under what you explained?
And may I ask where do you have this information from? / Where can one read more about this (specific behavior for the Fuji)? As the manual only states regarding shutter priority: "Shutter response is prioritized over focus. Pictures can be taken when the camera is not in focus."
EDIT: Ok just read about phase and contrast detection. And found the place in the manual where it shows phase vs contrast focus points (p. 79 if anyone is reading) Is it correct that the focus points in the centre are all hybrid?