No, it is not a logical fallacy because it demonstrably was, and, to a degree, remains true to this day. MS-Windows' biggest problem, far-and-away, was all users running with Admin privileges. Even when they finally addressed this in MS-Win7, they gave users an easy way to override it--which, trust me, most did. (Because, you know, the O/S asking "Are you sure this is a good idea?" is an annoyance.) The problem was exacerbated by the fact that, even as late as MS-WinXP, when there was finally a clear delineation between administrators and users, many of the apps were so-poorly designed they had to be run with Admin rights. (Some of those were Microsoft's own apps, too.)
Yes, it is true: MS-Win was also most-exploited because it was the most popular. But it was also most-exploited because it was the most-easily exploitable.
Tell me: Does MS-Win10 still allow users to dial UAC down to "zero"?
*nix' (Unix, Linux, the various BSDs, Mac OS X) are also safer because they are an inherently safer design.
And, of the two, which would you guess is referred to by many as "the new MS-Windows?" (Not as a reflection of its popularity nor as a complement, either.)
That is demonstrably false. For example: Years ago there was a guy who put a BSD system out on the 'net. An OpenBSD system, I think it was. He challenged the world to break it or break into it. There may have been a reward, but systems crackers don't need no steenking awards. I'm not 100% certain, but I do not recall of seeing, hearing, or reading that the system had ever been compromised. (To this day, OpenBSD retains the reputation of being the most secure general purpose operating system available.)
I've had servers, too many to count over the years, on the Internet since the 'net became commercially accessible. I've so far (knock on wood) yet to have had one compromised of which I'm aware. And if you don't think the bad guys have been taking shots at them, I've got gigabytes of logs to prove otherwise
Nobody in their right mind exposes an MS-Windows machine, desktop or server, to the Internet without some sort of firewalling. Unix and Linux systems perform as firewalls.
In your house... that's precious