This is still the argument for software copyright. And I think it's still a pretty persuasive argument, despite the success of FLOSS. To this day, there is very little successful consumer software. Outside of browsers, Ubuntu, Libre Office, and GIMP are more or less it, at least outside certain niches. And even they are a pretty tiny compared to Windows/MacOS/iOS/Android, Office/Google Docs, or Photoshop.

The browsers are an interesting case. Neither Chrome nor Edge are really open source, despite Chromium being so, and they are both funded by advertising and marketing money from huge corporations. Safari is of course closed source. And Firefox is an increasingly tiny runner-up. So I don't know if I'd really count Chromium as a FLOSS success story.

Overall, I don't think FLOSS has had the kind of effect that many activists were going for. What has generally happened is that companies building software have realized that there is a lot of value to be found in treating FLOSS software as a kind of barter agreement between companies, where maybe Microsoft helps improve Linux for the benefit of all, but in turn it gets to use, say, Google's efforts on Chromium, and so on. The fact that other companies then get to mooch off of these big collaborations doesn't really matter compared to getting rid of the hassle of actually setting up explicit agreements with so many others.