Actually, the very real Windows 8 fiasco was due to a crappy UI implementation.
After 16 years of constant desktop GUI (since Windows 95), professional training and all, professional qualification on Windows in corporate environment and stuff, the team of idiots who decided to impose the tiles and dispose of the Start menu is an irresponsible bunch of loonies. I hope most of them got fired.
Nevertheless, the idea to have a unified OS between devices is in itself valid. Windows 10 is a demonstration of what should have been done with 8 : leave the desktop alone, but make room for tablet computers. When tablet, use the tiles, when desktop use the good old Start menu and mouse just like all times. From what I understand, Surface sells very well, and the uncanny resemblance of the iPad Pro seems to show the concept was not that bad.
Now Apple has not done its own revolution here. In spite of the similarities with Surface, iPad Pro cannot use a mouse or a trackpad. Steve’s long shadow or not, OS X disguised into iOS remains input devices neutered. Sure, it is one and kinda the same OS, but made to be strictly incompatible between desktop and mobile.
When Windows has all these convertible machines growing in number, there is still iOS on one side, and OS X on the other. No mouse on iOS, no touch screen on OS X.
And let’s not forget the most used system of all, Android : a tablet fitted with an HDMI screen, a keyboard and a mouse, has little to envy a convertible PC.
Apple is between two stools at the moment. I am sure if and when the time comes, they will present the joining as “revolutionary” !