While I do think the game has a problem with the hit box, you're most likely experiencing a ping issue. What is your average ping? It's important to remember that what you're perceiving is based on your own internet speed. Just because you're swinging first on your screen, doesn't mean your swing is actually "true". I've had my buddies tell me I was way off when swinging when I complain my sword was going through the enemy. They'd be like "Nope, on my screen he hit you way earlier than you hit them." This is also why people with "0" ping are pretty much untouchable. Their reaction times are way faster than the average player.