IMHO,

Windows has completelly stopped its trend of becoming less shit over time and has actually started going backwards.

Modern Macs (having used both, I would say they aren't really direct descendants of the original Macs but rather they're major redesigns) already started at a point when usuability could be done better, kept improving for longer and, even though they stopped improving in terms of usability, unlike Windows they haven't gone back.

Linux is the only one that still keeps on improving (though usuability-wise it started ever further back than Windows), though slower than the others and often in a two-steps-forward-and-one-back fashion, so it's about to go past Windows (one might stay that it has already done so in usability and is only the large number of Windows-only applications that keeps Windows ahead) and hopefully will eventually pass Macs too.

Whilst what I expect for Linux has a big dollop of hopefulness, for the rest I think it's pretty obvious that Windows has never surpassed Macs in terms of usability and will never do.