I grow weary of those who see a weapon pointed at a canted angle as ignorant. Those who see a weapon not presented at a 90 degree angle see this as an ignorant thug level of weapon presentation. So far from the truth is such ideology.
When shooting from a weapon-side unsupported presentation, most folks are at a disadvantage. Human physiology dictates proper stances and holds. Stand easy. make a fist, and bring your hand, strong or support side, and bring your fist to your eye level, Your hand will naturally come up at a 45 degree angle. Using both hands will present your sights at a 90 degree angle. Using your weapon hand unsupported will bring your sights to a natural hold of 45 degrees. If not, the military training of a 45 degree stance would be un natural.
Using both hands brings the sights to a 90 degree angle. most times, the weapon hand is at a natural 45 degree angle relating to the sights. THis works well when utilizing a ballistic shield, or available effective cover.
Most importantly, most semi-automatic weapons present a very effective sight pattern. Take the Glock, or 1911, or most semi-automatic weapons and you see the same sight picture, equal distance of bad guy on either side of the slab sided weapon and press, press, press. The trigger is never pulled, it is pressed. Too far on the pad of the trigger results in a pulled shot, to little results in a pushed shot.
Sights are not as significant at ranges less than 25 yards if the weapon becomes 'one with your hand.' Make your adjustments according to the situation at hand, and there will be success. AS has been said here, you can shoot often, and shoot rapidly, but only hits count.