There's a significant flaw with this argument, however: it assumes that Nokia's switch to Windows Phone began or accelerated the company's decline in market share. As if Nokia would have been better off sticking with Symbian.
The truth is that Nokia's market share plateaued in spring 2007 -- coincidentally, right around when the original iPhone launched. The pre-Elop management was determined to ride Symbian into the ground, and there's a real chance that Nokia would actually be worse off than it is now.
I wonder what would have happened if Nokia had gone with Android. There is a chance it would have fared better, although I'm not sure that would be healthy for the industry as a whole. It would have likely sounded the death knell for Windows Phone. After all, HTC, Samsung and their kind still treat Windows Phone as a side project (at best). We don't need any more of a smartphone monoculture than has already emerged so far.