No, this has nothing to with reacting to any change. Multiple people have stated that the sidebar now looks like 2 levels of hierarchy - the icons being the 1st, and then the text being sub-categories of the icon. Which of course is not the case here. I like the dark sidebar - it looks nice - just not the separating of icon and text. It makes no sense.
Also, why fix what wasn’t broken - and leave tabs/notebooks still broken?