I'd argue that the central mistake was the decision to radically change the desktop experience to conform with the touch experience. I.e. the radicalism was it

I'd argue that the central mistake was the decision to radically change the desktop experience to conform with the touch experience. I.e. the radicalism was itself the mistake. My feeling is that Apple made the right call here: Desktop and touch interfaces are different enough that you just have to write different code for each.