Err Windows contain a very good antivirus by default. Its actually better than anything you can buy.
Not only that - but using Google-only products drives you to an ecosystem that is going to be worse than Windows ever was.
Arguably, Windows, will all of its shortcomings was and still is pretty damn open.
Not in code, but in APIs, tools, etc. That's actually how it won so much marketshare in the 90's. (its now also getting more and more open in code, tho).
ChromeOS on the other end, is pretty closed. You want a kernel driver? Dream on. If you don't make your own hardware, or don't use Google-approved hardware, you're out of luck, it will not work and you can't make it work without rooting the machine (ie you can't sell or even give away that product to customers).
You want to customize some API? Dream on. This one is impossible without replacing the OS.
All this is trivial on Windows (and regular Linux, or even OSX, for example).