You have to understand, Killjoy. They aren't hacking my friend!
They are wearing heavy armor and using 2 handers. You can do the same thing man, adopt the mantra of "no-block-only-hit", get some heavy armor and a long 2 hander and start swinging.
Also, some of them are cav. That's completely OP.
The others are archers/xbow men, more OP classes.
The rest of them are shielders or polespammers (or both!). Very very OP classes.
The ones that aren't in heavy armor are OP agi characters, which everyone knows are OP.
Then get loooong hours in of practice and having fun while you play, and you got yourself a seven course dinner of OP'ness.
That, and they hack.
TL;DR : Get yourself a 2 hander, 1 hand/shield, Polearm, Bow, or Crossbow. Get a horse, or play on foot. Get your self some heavy armor, or some light armor. Stack your strength, or your Agi. Practice a lot, and have fun with friends while you do this. Then you can hax too!