Why was it a waste of time/resources? From all we know, the X might even sell better than the S, the preorders are crazy. Which would make Tesla a much larger company than selling the S only.
Without knowing many of the details of Tesla this argument makes sense on it face. That being said there's a hefty amount of hindsight going into this analysis and I'd respect it more if the author made this call about 2-3 years ago.