Not the author, but perhaps they meant that the UI was sluggish to use?
I find OSX great if you have one browser window open, but start to multitask at all and I personally find it a real pig to work with. Open windows are hidden behind a tiny white dot on the task bar, lots of wasted space around the task bar, no snapping or window-splitting, the menus are detached from the windows they are for and you need to focus the window to get the menu to appear, the task switcher thing (expose?) is a horrible jarring swooshy animation that is awfully distracting with things moving around on the screen on their own as you are trying to look at them.
I find it so frustrating to use after almost a decade of using macs now - it does not get any better once "used to it". Linux (Cinnamon or Plasma) + Windows 10 are just so much more intuitive for me. I'd 100% bite the hands off of the IT team here if they offered me a Windows 10 machine instead of a mac for my engineering laptop.