Is simple because sword attacks are a minor part in his SCV moveset,and are supposed to be slow but powerfull (so are not to use at random,but in particular situations),where most of his moves are made with wrist blades,wich are very fast,various and reactive
About the AC part,the game is sloppy,his combat system is sloppy. Ezio concept is't about being sloppy or weak in direct fight. Use the sloppy game engine to judge a char is logic bs,so the cutscene show how Ezio is supposed to move/fight in his creators mind, the character concept