GIMP is awful compared with Photoshop.
You are of course not the only person to say this, but GIMP comes at a much better price, and certainly has its adherents. I wonder if it is more a question of familiarity (as you allude to below) than essential functionality.
Writing novels doesn't take much software. You can do that with a latex editor and the sffms class.
For that matter I've known of people writing a novel with VI. Your statement oversimplifies a little, but my point wasn't that Linux was better for novel writing, only that Windows or a Mac was not a necessity. By the way, the very popular novel-writing software Scrivener now has a Linux version in beta.
Outlook for example isn't a 'niche' app, it is a basic workplace necessity in almost every office.
I wonder if you are equating "commonplace" with "necessary," although the two categories merge when (as in the discussion in postings above) compatibility becomes an absolute requirement. Otherwise, Outlook is not a basic necessity by any means. Email, contact management, etc., can be done in a lot of ways.
Having a Linux near equivalent is better than nothing but nobody is going to start using Linux to have something almost as good as whats on windows. In mot cases they won't even switch for something as good or better, they want the apps they've already invested time and effort learning.
You are correct, but this has nothing to do with the inherent superiority of either Linux or Windows. It has to do with the vast inertia created by a near-monopoly provider.
In my previous employment, I was once asked by a group which I had just taken on as manager if the rumors were true and I was going to dump Windows and replace it across the board with Linux. For the reasons you mention, I had to say "no" because it would have been a poor business decision. That's really unfortunate, but reality is not always friendly. However, I didn't up the ante by bringing in every new Microsoft product as it rolled out the door.
After I moved on, though, my successor certainly did, declaring, "We're a Microsoft shop. They make good software. We're going to use it exclusively." Well, that's a business decision; what can I say?