I am sure what he means that is we lost a lot when it become unprofitable for companies to offer solid UNIX offerings that were supported in the way he would like. Other than the fact that it evolves glacially, Illumos is in an even worse position than Linux when it comes to offering support.
If we are being honest though, in the terms that this article is arguing, "Linux" as an ecosystem is the wrong label. When it comes to stability and support, we need to think of each Linux distro as an Operating System. In that sense, things like RHEL are certainly well supported--including on the desktop. If your app targets RHEL, you pretty much have none of the problems discussed in this article. You still have a smaller universe of applications than Windows of course which is to be expected.
So, the problem boils down to "nobody is making sufficient money off desktop Linux to steward a desktop Linux distro". That is not careless devs or bad design decisions though--no matter how chicken-and-egg you try to paint it. It is simply the network effect.
Decent desktop operating systems exist and they already have large application universes and large, monetizable user bases. They appeared into a vacuum that lacked such operating systems but that vacuum no longer exists. That makes it almost impossible to economically introduce a new desktop platform. Certainly none of the commercial attempts have succeeded in the last few decades. In fact, the system that has been the MOST successful is Linux. By that metric, saying that Linux is doing it all wrong does not ring very true.
Valve is doing a lot to make Linux gaming a reality because, when it comes to the network effect, it is largely true that Steam ( not just Windows ) is the true platform. So, if you can bring Steam to Linux, you can move the users there too. It is still early days for that but it appears to be working.
On the mobile side, the network effect is very much alive as well. This is why Windows, using of course all of Microsoft's tricks, strengths, and knowledge, completely failed while the Linux kernel ( in the form of Android ) has totally dominated. And that is not for any of the reasons cited in the article. Do you think an Android app from 2008 will run on Android today unmodified? An iOS app from 2008 on iOS today? I don't think so.