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!)