Its not about brand dilution--its that the most efficient environment for complicated apps is NOT touch, but pointer (mouse/trackpad). Remember, MS was very aggressive in pushing "modern/touch" ui and apps and the user base rebelled. The desktop was "legacy" in windows 8. Now in windows 10, the modern tile interface is "legacy"--subordinate as part of the start menu on the desktop
First, I agree about complicated apps - I just opened Pixelmator on my rMBP and there are lots of tool boxes with tiny click targets. Of course, Pixelmator Team also has a well-featured IOS version, and it'll be interesting to see how it compares on the IPP versus OS X. But I couldn't imagine using my fat fingers to navigate the OS X version of Pixelmator, or any relatively complex piece of software. Mouse and pointer are where it's at.
But don't diminish how much Microsoft worries about the Windows brand. When Apple released a music player, it wasn't the Apple Music Player or Mac Music Player, it was iPod - completely new branding. When Microsoft released a phone OS, it was Windows Phone, even though there was very little "Windows-ish" about it. Everything Microsoft does with OS branding is Windows-something.
Windows 8 was Microsoft's attempt to play in Apple's end of the pool. It was, "Developers, come write apps that are touch-first, and we'll help promote 'em, sell 'em in the Windows Store, and limit side loaded apps, just like Apple." Developers said, "Nah, we'll stick to desktop apps, thanks." Users were confounded - and the Windows brand was damaged, probably more than by Windows Vista (and actually, I wasn't that put off by Vista...)
So they retreated to their side of the pool and regrouped. And Windows 10 is an excellent OS, fun to use, and as you point out, pointer-centric. But that leaves Microsoft without a real, touch-first platform. Does anybody use full-up Photoshop in touch mode?
So MS best option was to leverage the depth of the Windows app infrastructure and release a device that works best as a laptop replacement but can perform tablet functions. Apple, without the depth of the app infrastructure, elected to create a new OS, not leverage the Mac name, and depend on the developer community to fill the app store with beautiful, complex apps. Full-up Adobe Creative Suite? Nope, and if your workflow depends on them, look elsewhere - OS X or Windows, probably. But I am interested to see what app developers do with the Apple Pencil - now you have a touch device that's as accurate as a mouse...