Android/IOS tablets do not count when measuring PC OS market share - they are not classified as "personal computers" and cannot be factored in to market share statics. I'm not arguing that Android/IOS tables are eating into PC market share - they absolutely are. But that just shrinks the overall market, it doesn't much change who dominates that market. For a car analogy, saying Android/IOS tablets sales are dethroning Windows is like stating a surge in bicycle sales is stealing market share from Ford pick-ups. I assure you, Scwinn has nothing to do with Ford's slipping position in the light-duty truck market.
All statistics that you can find on various sites show that each of Windows XP, Windows 7, and Windows 8.1 individually hold more market share than all non-Windows OSes combined. On some sites, Windows 7 by itself holds more market share than all other Windows versions AND all non-Windows OSes combined. No non-Windows OS even comes near 10% market share.
"Reign supreme" means to dominate. Windows CLEARLY dominates PC OS market share. To claim otherwise just shows your ignorance.