I see more and more people - and not just hardcore devs - using Linux.
For me, Linux has been a better desktop experience since around 2005 sometime: faster, easier to configure to my exact liking, easier to install, less hassle to maintain. (Except the time when KDE 4 was new and Ubuntu changed to Unity.)
For a long time I even though it was just a matter of time before everyone would realize but now I have realized that people are just different. Some people actually like Mac and Windows. Some people are driven mad by inconsistencies in my favorite DE (KDE) that I cannot even spot after someone tried to point them out. I however can't stand CMD-tab on Mac but Mac users - like me with the alignment issues on KDE - cannot see how it can be a problem.
Summary: it is not like any of them are way ahead in general. I see more and more people using Linux and expect numbers to rise a few percentage points more.
It depends on what desktop environment / window manager you use.
I don't notice too many weird issues when I run i3 and bsp on my Linux laptop. I think the nice thing about a tiled window manager is if you go down this route, you often hand select a bunch of small components that do 1 thing very well. Even going as far as evaluating and picking a specific compositor (or maybe not even using one at all).
You are right tho about Windows. Its UI is very stable and buttery smooth for actions like moving and resizing windows. It has a level of polish that out of the box DEs on Linux usually don't have.
https://sourceforge.net/projects/linuxfxdevil/
https://b00merang.weebly.com/windows-10.html
Leveraging the FOSS work and cutting down on maintenance costs, and focus that only for LSW, to guarantee the functioning of that abstraction layer, and leave the harder parts (hardware support, security etc) onto public to pick up - at the cost of a few coupons, t-shirts, coffee-mugs etc thrown at them via "hackathons". (And even perpetuate the "passion for software" hence "public github contributions". May be give a slightly higher tier github subscription for free, they've bought that org anyway. And people are anyway suckers for Internet points)
ReactOS has been a thing for 20 years now and it just isn't that popular.
Second, MS would need to port some sort of compatibility layer, which would probably be 10000 person-years to achieve anything like the backward compatibility they currently support.
Third … well, that would be it. The vast majority of non-techies would be ecstatic to find they can upgrade for free for ever, their software would just keep running, and hardware would work basically from day one (because the companies developing cutting edge hardware Windows would pivot their driver development) until the end of time (because FOSS drivers, while slower to appear for most hardware, are supported essentially forever).