Why are Warlocks so OP?

So looking over the new Warlock class, everything looked fine until I noticed the Eldritch Blast power.

This is, obviously, the Warlock base attack since all warlocks get it, and it seems overpowered compared to most of the other character classes.  It has a range of 50 feet, does a base damage of 3d6 and adds the player's INT bonus to this.  That's the equivalent of a ranged rogue sneak attack every round.

What's the offset for this?  It costs nothing to use and does a whole mess of damage, and scales as the Warlock gains levels.  I'm missing what the problem is here.
In our playtest, it was very powerful, but we did not see where Int modifier is added to the damage.
Yeah, don't add the Int mod to damage.  There's a bunch of threads about it.
No intelligence modifier to damage. And 3d6 force damage can be pretty high but it can also be really low. It averages out to be a little less than what a Fighter dishes out.
I don't use emoticons, and I'm also pretty pleasant. So if I say something that's rude or insulting, it's probably a joke.

"What's the offset for this?"

The terrible burden of the wart.

Sure, fighters may do less damage and expose themselves to more danger, but at least their skin is unblemished.

No intelligence modifier to damage. And 3d6 force damage can be pretty high but it can also be really low. It averages out to be a little less than what a Fighter dishes out.

This. EB briefly outshines the Fighter when it bumps up to 4d6 damage, but then the Fighter gets a second CS die and retakes the lead.

In our game, the warlock only hit 2 out of 10 tries so nobody thought it was overpowered :P

 
It's funny because I think that, in combat, the Warlock is rather underpowered.  I mean, they're amazing utility what with rituals and charms and whatnot--Fabrication of the Weave is up there with Ghost Sound as my favorite utility magic--but in combat, pretty much all the can do is (maybe, if they took it) cast an inferior Thunderwave (because Deafen is worse than knockback) twice and spam Eldritch Blast.

Eldritch Blast does 10.5 damage on average (no, you absolutely do not add your stat mod to it, or to any spell, and I don't know why people keep misinterpretting that given any context at all).  That's good, but not amazing.  Especially considering he has to stay at range or suffer serious attack penalties.

The Fighter with a shield is likely to spend 8.5 average damage, but tout 50+% more HP, an AC 4-5 points higher, and have the option to deal +1d6 more damage (12 average) or take 1d6 less damage that round.  With a two-hander, drop the AC by 1, but pump the damage up by 2 (10.5 normally, 14 with Deadly Strike).

I could go on, but the point is that nearly every class can equal or out damage the Warlock, and, excepting the Wizard, can do it with a better AC and more HP.