Is Linux usable as a desktop alternative to Windows or Mac? Absolutely. I'm living proof. I've been a Linux user and developer at work for 20+ years. I've been a Linux user at home for over a decade. But I'm a sample size of 1. It comes down to effort - both real and perceived.
A significant percentage of people currently using Windows at home use it primarily for web browsing and email. A significant percentage of work use involves that and typical office applications such as Word, Excel, and PowerPoint. Linux on the desktop is entirely capable of assuming these tasks. However there are two gotchas.
One is simply the barrier(s) to entrance into the Linux world. Want a new laptop? You can find dozens from major manufacturers or sites like Amazon or New Egg, or at local retailers like Best Buy - almost all running Windows, A relative handful running some version of Mac OS, maybe a tiny fraction offered with Linux. The upshot is, if you want to run Linux it is going to take a little work, a little extra effort. While you can easily get Win/MacOS ready to run out of the box... For most users and most devices a Linux fan would have to figure out how to download and install Linux themselves. Why bother when the computer is ready to go as is? So that extra work, minimal as it actually is, represents a significant barrier to entry. You have to really want to run Linux. Pro tip - it really isn't that difficult to download an ISO image of a popular Linux distribution, copy it to a thumb drive, boot from that thumb drive, and install Linux. It is a few steps yes, but once you understand them it is easy.
The second "gotcha" is simply the pervasiveness of Windows and MS Office tools. Even if you're a Linux fanboy, either recent convert or long-time aficionado, chances are you're going to have to work with or interact with generic Windows users. As good as the Linux applications are (eg. Libre Office) when interacting with their MS counterparts there are sometimes, perhaps even often, issues with fonts, layouts, etc. It represents an impedance mismatch that seems perennial, perhaps even pervasive.
The upshot is, given MS's position - basically having gotten there first - they are going to be the desktop, like it or not. This relegates Linux and Mac OS to basically also-ran status on the desktop. Attackers looking to skim/scam information have got to play the odds. I won't even touch the relative security postures of Win/Mac/Linux. If you want to attack systems, you play the numbers. The numbers say you'll find more, many more Win systems out there in the wild than you will anything else. So that's what the attacks are generally written for.
The Linux base distro is never the problem. They are great. I’ve been running a version of Linux since 1993 or thereabouts.
It’s always about the apps, or lack thereof.
Sure, open-source crapware exists. Hard-to-use crap interfaces (that’s a open-source trademark, even if running such apps on windows or a Mac)
Glad you mentioned Open/Libre/ shitOffice. Fonts, themes, animations, transitions all don’t work (PowerPoint), no VS Basic support for Macros (Excel), and the same font and layout issues with Word. No Camtasia support (huge one for me as a content producer. Funny the Google stuff doesn’t have these issues... and there is a good MSOffice version for Mac. CrossOver office is a poor substitute.
And content-creation is worse. No out-of-the distro support for any Abode, Autodesk, Game Engine Development or other normal apps people will run as a content creator. You client needs PSD files or illustrator files. Not gimp. You need to export to fbx. Nope again. Clients won’t take blend files.
So if Linux fanboys really want Linux to takeoff with desktop use, they need to get app developers that every one else uses to support app ports to it.
But as you said “this is the year of the Linux desktop” has been said for almost 20 years now.
Windows gained popularity while Linux was still mostly command line use and didn’t have much of a desktop. Hence businesses used windows and people wrote business programs for windows. I was in the sign business for years and there’s no way a Linux machines could be used for that because all the sign layout software, cnc and plotter software is written for windows.
That being said, I’ve been using some sort of Ubuntu distro as my PS OS for 15 years now. Still, if I want to use my usb scan tool to diagnose a vehicle or use repair info software, I have to reboot to win7 pro.
Aside from publishing design/layout software which is often Mac, pretty much every other specialized business software is MS Windows.