2. Puss does not have proper experience. He is not a soldier. He is not a fencing academy graduate. He is a self-learner and that's a crucial detail. In the movie we see him practicing only with imaginary opponents. In the Netflix show at least it was shown he got trained by El Guante Blanco, but seeing that it isn't regarded as canon, we have to let it pass. You literally can't get really good with fighting a sword if you only practice against imaginary opponents. You'll need an instructor who will show you the ropes and a duelling partner against whom you can polish your skills. A punching bag doesn't punch back. The Polish and Lithuanian nobility, however, practiced every day because it was both their hobby and duty. Those who were preparing to join the Polish Hussars' ranks practiced even harder, since they were the ranks of the elite horsemen.
Puss is able to defeat guards and criminals, that's a given. However, guards are meant for law enforcement, not fighting. Same for criminals - they'll mostly flee once they encounter lethal danger. He was never seen fighting professional soldiers, let alone elite units, and this was for a reason - he just wouldn't handle them. Lucky him.
3. His hat is not made for sword fighting. We see his cavalier hat which is his signature head cover. It's not madfe for sword fighting at all, since it restricts his vision, it's wide and broad, and could fall on his eyes while fighting. This type of hat was actually made for marksmanship among musketeers. The wide round of the hat was placed inbetween the lit fuse and the face by bending the head forwards, just so during firing the burning hot gunpowder doesn't explode ino the musketeer's face, causing discomfort. Instead, it just lands on the hat and the musketeer is left without any pain.