Although, people at that time were superstitious, there were left-handed warriors too. Probably, this would have been completely different among Catholics, who persecuted lefty people for being cursed (because the Devil was guiding their left hands while fighting).
When it came to fighting, the left-handed person had a huge advantage. He was able to defeat right-handed fighters who were actually much better than him (just as a left- handed tennis or fencing player today has the advantage over the right-handed counterpart).
Nowadays, many scientists believe that left-handers could have a fighting or sporting advantage, but it isn’t a question of speed. Actually, left-handers may possess enlarged right hemispheres, giving them spatial skills.
Apparently, the advantage is more tactical than neurological. You can get more information about this in here: