You may have a point but I am more inclined to agree with the authors in that it would have been a smarter move to warn Syria first.  Tin-pot dictators are megalomaniacs to a man and are more likely to respond to unexpected aggression by striking harder  next time.

Men like Asaad and Kim Jong-Un are even more unpredictable than Trump since their grip on reality is even more tenuous. While a warning might not have deterred Asaad, it would have counted for something with Putin; similarly, if the US strikes North Korea, China would be less likely to counter with a hard strike if a warning comes first.

The final point is that the United States would do well to just stay out of the Middle East entirely.  Their shenanigans over the past 50+ years have made the region less stable, not more so, and it is my contention that more people have suffered and/or died through their actions than saved.  What's more, their interference in this region is the biggest reason for Islamic hardliners.