I've also died many times because the enemy was a locker who hit me thanks to his lock that made his hit way easier, blocked my jumping, or prevented me from going on his sides.
And once the locking warrior has come in range to hit you, it's your turn to have to dodge his attacks and to success to get away from him. If the archer tries to run away, there are high chances he gets an hit in his back. If he attemps a jump over the enemy, he still can be hit. You can also do

And as for having problems lockers, I often have because i get stuck into them way more often than with non-locking enemies, but it's maybe because my dark messiah is very buggy and i'm a special case.

Assassin, stealthed or not can get shot from a distance by any arrow. He also has the change to avoid it or that the shooter misses. Better the shooter, higher the chance to hit, no matter the opponent's skill of attempt of dodging. Same goes for Warrior, if he chooses to run with his shield up all across the map, he won't run that faster than the Archer can. He will lower his guard in order to get to the Archer. You have the window of opportunity to shoot, if you don't, that's your mistake, not his good skill of seducing you otherwise.
About the terrain that the attack can use ... it's not the attacker that chooses the combat's ground.

As for the rest ... I've died countless of times by people who Locked-On me, and I've died countless of times by people who don't ... and I've killed both Lock-On'ers and non-Lock-On users even more countless of times, yet these are still not good enough reasons for promoting it or dismissing it.

And I will stress it again, what was it 142th time? Melee combat in Multiplayer games is extremely hard. Lock-On is used for that exact purpose, and I will support it until Lock-On also gives you invulnerability and 1-shot boost attacks.
I won't even bring up WoW into it, but I bet that in Guild Wars's PvP system you also have something like "players can move through other players" system, making them unable to hit each other because Multiplayer interactions are unpredictable and not able to use with ease, or anything similar to that.
And since this is an FPS game, where you can't make people move through each other, Lock-On is the next possible options, for Melee users that is.

And if you want my opinion about it, not as a neutral observer, I can tell you that I don't see Lock-On being overpowered and bad, nor do I see it as such a huge advantage (when we speak about good players only). I won't mind people removing it and I won't mind it staying.
May it be for the whole server or just the Clanwars rule.