Not exactly true. for example, I was playing with Debian based Corel Linux in 1999. It was a full-featured OS and being that it was from Corel, even included WordPerfect. I could network it to Microsoft OS based computers, read/write to their file system, surf the web, print, send faxes, you name it.
It was ready, but folks just weren't.
From Wikipedia...
Corel Linux, also called Corel LinuxOS, was a Debian-based operating system made by Corel that began beta testing on September 21, 1999[1] and was released to the public on November 15, 1999. It mainly competed against Windows 98 and Windows 2000 by Microsoft, plus Mac OS 9 by Apple.