You are right, I abused the hyperbole. The IBM investment was not the first thing that propelled Linux to the mainstream. I remember that in 1999 my university was already installing Red Hat with Gnome 1.0 on the workstations for the computer lab, which of course already implies that Red Hat already existed as a mature company trying to make money from support contracts.

But even if the data point is not good to support the argument, I don't think one could argue that Linux succeeded by "being free". If Linux was a "serious threat" in 1998, it was because there already companies looking into it and willing to make back it up financially to help its development.