A thousand years ago in Portugal it would seem to be an advantage. medieval times were noted for men who were short tempered, violent and thought in black and white terms. Would make for a loyal retainer or a good crusader.
That would work, up to the day where he misreads/misjudges a situation and ends up injured or dead. But then, in the Middle Ages, you needn’t have had Klinefelter’s for that to happen, anyway.