Re: It is remarkable that Windows 7 [...] while maintaining [...] 27 per cent market share
No, not really. I use KDE (Neon) on my 4GB RAM (non-upgradeable) cheap laptop, with its Intel Atom-derived Pentium CPU (probably the hundredth iteration to receive that name by now), and it runs great-- I use it every day as my grab-n-go laptop.
KDE used to be a lot heavier on resources than it now is. Things have changed, bugs have been fixed. It's a whole lot better than it was a year or two ago.