That's granted. That's selection step 1. Then UNIX cum Linux approach eats the world for a couple of decades, pulling its weight. If it was inherently flawed, if SoTA approaches were addressing inherent issues, then it would have failed selection steps 2..n. And we would have long ago bitten the bullet to replace the "lucky" legacy. So, yes, the lucky contender has issues, has warts, can certainly benefit from x, y and z, but as is, it continues to be viable at scale and that is not "luck".
Second, we simply don't know, considering all aspects including human resources and engineering economics, whether Xerox, DEC, or IBM's alternatives would have fared better than UNIX. I'm open to learning why/how if this is a shut case in your opinion.