In the case of UNIX, it's not merely commercial success and popularity. It is the choice of a large portion of the smartest people working in technology. If we were talking about success amongst the hoi palloi (like, say, Windows), then your point would stand...but we're not. UNIX has seen its fortunes flounder and flourish multiple times over the span of 30+ years, and yet, today, UNIX runs the most important technologies on earth (Google, Amazon, the majority of all other web applications, the best smart phones, most smart devices with anything more powerful than a simple microcontroller, and a whole lot more), because the people building them chose UNIX.

So, is UNIX technically sound and superior? In the general case, I would say, unequivocally, yes.