Certain Classes seem to prevail in certain brackets in PVP moreso than others - some due to the availablility of new gear, a good synergy of recently aquired skills, a new talent available that pushes the gear over the top breifly, or a just plain numerical/logistical advantage over other players.
In my experience it looks like:
19 Bracket = Rogue/Hunter
29 Bracket = Pal/Lock/Mage
39 Bracket = Pal/Lock/Sham
49 Bracket = SPriest/Druid/War
59 Bracket = Druid/War/Rogue
69 Bracket = Hunter/Druid/War/Lock
70 Bracket = Druid/War
You'll notice some classes don't seem to make the list too often, but all of them touch it in at least one bracket.
Warlocks do not excell in a ridiculous amount of brackets - nor do they excell in the one that is truely important - the 70 Bracket. Playing often a pure DPS role in PVP (SL/SL being an alternative defensive logistics role) you'll find Locks play middle field compaired with other classes (looking in the top Arena teams will show you where we stand but we are technically no better than mages.)
As said, diminishing returns, Shadow resists, cleanses, totems, CoS, Feral, 3 Warrior abilities, WotF, Beastial Wrath, Bubbles, a Trinket, and lag all contribute to the gimping of the ability to use fear against ANY sort of real PVP opponent. Sure a Good PVP Lock can tear the crap outa almost anything if it's entirely Raid Specced, but that should be true of most classes.
In high end PVP (even in crowded AV matches) Fear will not work if the opponent knows they are fighting a Lock. What I still use fear for a breif save off another class in dire trouble (aka knock a DPS off a healer or something.) Even that only works temporarily.
In 1v1 Dueling, it's often possible for a Lock to use his multiple fear abilities to control the battle, but this will not work so well in any real PVP - and I can damn sure tell you that Dueling is not any sort of real PVP, especially at 70 - it may be some decent practice but certain classes are unbalanced at it.
I'd just like to clear up any confusion here, seeing as you obviously had a rough time I'm assuming you're either not PVP specced/geared, you fought in a duel, or your in a very low level bracket (in which druids tend to suck.)
Right now as it stands, Warlocks (actually Pallies/Shammies/HPriests) have every right to be all over the druid forums complaining because nothing stands up to a properly geared/specced/trained druid in 1v1, 2v2 or 3v3 combat - and on a field like a BG or in WPVP even if they are going to lose they have more ways to get out than a Rogue.