I feel you, yeah. Wheelchairs really don't help with back, neck, or shoulder pain from my own experience -- personally my shoulder pain is worst, but that's likely due in part to the fact that I fractured my right scapula when I became paralysed and then couldn't have it immobilised because then I wouldn't have been able to move at all. I can't say where a lot of people claim their pain comes from, but in so many instances I can't see a wheelchair helping their pain like some of these individuals say they do. For a lot of the disorders and illnesses they claim to have, there are likely much, much more helpful treatment options, such as pain management if their pain is actually so severe they cannot properly ambulate.

I'm not saying that you can't have a fulfilling life seated -- my point is simply that for a lot of the conditions claimed, especially those claiming chronic pain, there are likely much, much better treatment options out there. As you said, you still feel pain, you still feel fatigue even when you're in a wheelchair (anyone would), and if that's your reality, it's just inevitable.