The smoothness thing is actually an architectural choice. On Windows and iOS, the multitasking subsystem will stop the world for a user gesture. On Android it treats a user gesture as one task to handle among many.
Well frankly, it seems like Android made the wrong choice. Going completely unresponsive is completely unacceptable.
That's certainly true now, and the Android team is on record regretting the decision. It would have been the correct engineering principle for a general purpose computer but obviously fails for a consumer content consumption node.
Currently both the core team and OEMs are striving hard to work around it (reversing it would be impossible as it's baked in).
However, I think as mobile platforms increasingly take on the role of general purpose computers, it will actually end up being a net benefit, and Apple's decision will look as short-sighted as the lack of true multitasking in older Macs.
But maybe not? Who knows...
I hear later versions of Android did get smoother on flagship phones, but I don't know how or if that translates to lower-end devices.