Downward slash at the cockpit? Someones guestimating a little bit. Add the velocity of Shinn's attack plus the LARGE difference in strike range of Shinn's anti-ship sword vs Kira's beam sabre and then calculate Kira's use of his shield. Kira was using his beam sabre in much the same way that pikes were used against enemies on horseback, in that Kira was hoping to lessen the damage by using the enemies momentum against him. However, If you notice the placement of Shinn's attack and Kira's placement of defense, there was no room for a 'downward slash' otherwise his defense would have been lowered and he the risk of him dying would have risen. So that's out.

As for Shinn = Kira in comparison to piloting ability, take into account the fact that Kira has been a pilot much longer than Shinn and that Kira was essentially bred to excell over others when comparing. When that comparison is made, I believe that even most Shinn haters should be able to admit that Shinn has increased in ability drastically in a short period of time. The major difference in the skill gap between Kira and Shinn is a simple matter of style: Shinn always aims to defeat the enemy as quickly as possible (that being the cockpit), while Kira aims to disable. Yes, Shinn had the advantage because he knows Kira doesn't aim to kill, however this comes at the old "Low vs High ground" theory, and raw skill isn't the only thing that makes a good pilot.