The modern Mac is blazing fast hardware. The UI however still has a lot of ancient baggage which drags performance down. I am running a PC game on my iMac that is written in Direct-X at full frame rates via Crossover. Metal is incredibly fast access to the GPU, yet the Finder is still lame at doing lots of things. Like any 20+ year old technology, it's a combo of old baggage holding on alongside massive improvements. Windows 10 is no different, just in different ways. I do wish Apple spent a little more time on general performance and usability improvements (looking at you Xcode) but I know supporting a massive codebase with such a long legacy is really hard.
That said Apple doing their own hardware has always been the ultimate goal. End to end control was always the dream.