I can say, with some authority, that Linux succeeded on it's own merit, mostly because it supported a broad range of commodity hardware. It got a boost because everyone started buying 386s, which were the first competent hardware for the IBM PC. There were lots of options back in the late eighties, all vying for some kind of position, but most of them had big problems of community: Coherent, MINIX, xinu, Xenix, Apple A/UX, netBSD, OS/2, OS-9, QNX, Lynx, etc. I looked at all of them as reasonable alternatives to the laughable PC operating systems of the day (MS-DOS and Macintosh System 7). NetBSD was a reasonable competitor right up through the mid-nineties, but Linux hardware support eventually blew it out of the water. By 1995 it was clear that Linux and the open source development methodology had won handily.
Yes, licensing had something to do with all of this, but so did Linus' management style: people wanted to work on Linux, and Linus did not turn them away: he welcomed them. I wouldn't want to say anything bad about Dr. Tanenbaum, I have the greatest respect for him and his work, but other than netBSD, none of the other free and open OSs of the day were making any attempt to take the general market, MINIX included. I remember looking at MINIX and rejecting it because of it's limitation to academic use (the limitation to the 286 wasn't that much of a concern, though it probably should have been).