This does a great job refuting one of Pinker's fact based counter examples. It in no way refutes the core thesis of Pinker's review, that Gladwell is full shit.
The whole point of Gladwell's assertion is that if Pinker is this haphazard in gathering supporting data, perhaps his entire review is nothing more than opinion.
While there's nothing wrong with that - being a review and all - it certainly isn't a factual debunking of data.
(btw I'm not debunking the assertion, just your reasoning)
An honest reply would be to say: Pinker got everything right except this football thing.
In this case, the "everything else" is of much higher importance than the football thing.
Not necessarily: the key to getting a letter to the editor published is to make a single coherent point, and to express yourself well. A letter to the editor is not the right venue for a point-by-point refutation of someone else's work.
Why didn't he do it on his blog, then? Or say at the end of a letter: For a more complete response to pinker, see [URL].
We can conclude that he either had lots of other good arguments but chose to focus on that minor one, or that he didn't have good rebuttals for the other things.