Your analysis in #5 isn't strictly comparable. Intel fabricates semiconductors, ARM does not. Intel designs whole chips, ARM designs cores. To get good numbers here, you would need to separate out only the CPU design groups accounting information from Intel, or somehow isolate the integration and fab contributions of companies like Qualcomm/TI/Samsung/TSMC/etc... and add it to the "ARM" total.
But your broader point, that the desktop CPU market is at or near its peak, is I think spot on.