I do like the Black (for a very modest premium, you get some nice additional features, plus things like 'ethernet that isn't a slightly dodgy USB hack'; but its resemblance to the Arduino (aside from the 'capes') shouldn't be overstated.
Like the Pi, the Black is basically a full-fledged embedded computer at heart, not a microcontroller, so while it does have somewhat better I/O, it still doesn't bit-bang or do other time-critical microcontroller stuff without some very careful attention.
The PRU is one hell of a trick up the Black's sleeve when it comes to doing timing-critical stuff (no OS overhead, just like a microcontroller; but runs at 200MHz, so things that your microcontroller couldn't dream of bitbanging fast enough are within reach, plus tight integration with your spacious application processor and its tasty memory space, networking, etc.) Hand writing less-than-totally-copiously documented assembly code to get there, though, isn't exactly baby's first Arduino sketch.
I do find it rather surprising how much less buzz the Black gets (especially how modest the price premium becomes once you factor in an SD card for the Pi, and the more-or-less-incontestable superiority of the Black's specs); but using it for any sort of I/O that isn't tolerant of sloppy general purpose OSes is a comparatively advanced topic, though it is undeniably brutally efficient at such specialty tasks if you are up to it.