Fear does break quite often,
One, many classes can trinket out of it. Warlocks can dispel it, warriors and now hunters can be immune to it, pallies can bubble out of it, rogues can quite nearly prevent it from ever happening, Healers can dispel it off your targets as well, and last but not least stupid teammates can break it for you and get you killed.
Two, getting the cast off is trouble enough. Hunters, priests,(shadow or ones close to you) mages, warriors, rogues, paladins, shaman, and warlocks can all stop the spell from happening instantly, druids can intercept if they are good enough to anticipate it. Some are range dependent, namely rogues and hunters, but both have the tools necessary to work around it.
Hunters in every tree now have an instant ability to avoid being feared, with a 41 yard range and the ability to kite and daze they are now the strongest contenders vs being feared.
Shadow priests have blackout silence and fear themselves as well as heals and shield and shadow resistance.
Warriors have pummel, shield bash, intim, immunity, execute, intercept, charge.
Mages have counterspell, iceblock, poly, shields, dampen magic and mage armor
Paladins have shadow resist, repentance, HoJ, bubble, heals
Rogues have stealth, gouge, stuns, blind
Shaman have tremor totem, grounding totem, earthshock, heals
and of course ud have wotf and dwarf priests can share fear ward.
So you see, there are proactive ways to avoid fear and reactive. If you aren't going to factor it into your fights then you are the one at fault.
Furthermore, fear isn't much different then any other attack when you aren't ready for it. That 2.5k frostbolt, the Aimed shot that crits your pants off, the warrior that intercepts/charges and hamstrings you, the rogue that pops out of nowhere and cheap shots or ambush crits you for 2k+ is pretty much the same thing as being feared when you aren't ready.
I've been crit by SMITE for 1500, stunlocked by a rogue who popped a 90% resistance shield, killed in seconds by warriors who intercepted hit with hoj back to back 1500 crits, then pummeled, hit again, and executed, I was MOONFIRED for 900 the other day, and all of the points in the previous paragraph.
Every class is strong with the advantage, every class is imbalanced around another one or even two, one type of spec vs another type of spec can completely change the turn out of the fight.
But know this, warlocks generally dump 2-5 talent points just to make sure fear is 'a bit' more reliable, it is rare that I use it when I don't need it, the same as any other class's ability for them, if you think you will win hands down, you don't pop your 'overpowered' abilities.
The only class that has a right to cry about fear is druids imo, but it is much more fun to banish them anyway.