I don't know that firmware is the problem. The same sensor takes very nice shots on the BB DTEK60. With one glaring exception, the Windows camera app simply doesn't play nice with non-Lumia phones. That one exception was the One M8 which blew the Android version away. It wasn't a showstopper but it was markedly better.
If I was the type to wear tin-foil hats I'd say MS is keeping the Idol and x3 "in its place" on the imaging front to shine again with the Surface Unicorn. After all, apps and the general user experience being the same it would need something to differentiate itself from the herd. No, I didn't forget my meds today.