The point of gate isn't to go, say, gate in and charm or something similar. The use is that unless you're hiding in certain places, it gives them a place to start hunting you down. Whereas when they walk into the area there's usually plenty of time to get ready, but when they gate in you're fighting at their terms -- they know where you are, they have their spells up, and they have the initiative to put you on the defensive. Again, people like Tyrone can take the initiative that gate gives them, and run away with it.
Good pk'ers don't use gate as some kind of "one shot attack" that newbies are afraid of with illusionist and charm -- they use it as an alternative to walking in, and it's much quicker. No, it's not foolproof, and yes there is a normal spell lag to give people a chance to defend against -- but giving them one spell lag of preparation for the other people is much better than the 15 seconds of preparation that someone who checks his wheres constantly will have.
And if someone words immediately upon seeing gate, you know where to find them again. There's no escaping someone that's good when they have gate, unless you are completely paranoid about it and hide somewhere safe.