What do I mean by such a broad scale? Beyond what cameras can capture.
What 'cameras can capture' vary from camera to camera and from year to year, it's not that difficult a fact to grasp.
In both your scenario A and Scenario B there's no need for either HDR or XDR. You're not gaining anything by using either HDR software, automated blending software or manual blending with layers. It's a moot point.
You insist in being wrong Bob. Of course you are
gaining something with the HDR software and with the blending, you are
tonemapping the captured information, and that is the
gain you have, display in the output format all the input information. Something which has always to be done someway since capture devices are linear and do not perform any form of local contrast arrangements.
So what you gain using HDR software to tonemap a {-2, 0, +2} bracket from a 8 stops camera over a 12 stops scene using HDR tonemapping software, is exacly the same as you will be gaining by tonemapping a single shot from a 12 stops camera over the same 12 stops scene using the same HDR tonemapping software.
You suggest you will have no problem to process HDR captures when cameras can capture the entire DR of any scene in a single shot, andt there will be nothing to gain. WRONG, you will have the same challenges as you have today, the need to tonemap all that captured information.
Your conception of HDR, the 32-bit floating point formats (BTW there are many 32-bit floating point formats, you regard them as a unique standard that take part in the definition of HDR), and need of bracketing is conceptually errated. Perhaps your lack of math knowledge prevents you from understanding that the real problem of HDR is not the capture of information in a high DR scene, but its later processing to adapt it to the output devices.
Regards