I'd say that the momentum in the 1999-2001 timeframe was almost overwhelming, with a lot of buzz around the likes of Eazel and Helixcode, together with the excitement of Sun choosing it for Solaris.
It was certainly enough to push GNUstep/Windowmaker and Enlightenment into "also-ran" territory.
If Gnome 2 had come out a year before the dotcom crash rather than the year after, I think it probably would have definitively overtaken KDE as well. In the event, it didn't work out that way - and, as you say, KDE did enough to hang on (thanks largely to Konqueror!)
Meanwhile many of the folks responsible for those companies are now working with Microsoft and Apple technologies, which kind of tells how much they runned out of steam trying to make a useful GNU/Linux desktop.
KDE was going equally strong at the time though. Anecdotally, it feels like more people were running KDE 2/3 around that time period than Gnome. And while Gnome did get an overall user count boost from becoming the "enterprise Linux DE", that same thing also turned off some people, with projects like Xfce getting a boost. So I wouldn't say it ever really "reign supreme".