The straight up truth: Sort of.
Wizards not as much because they can attack so many targets with their at wills. Warlocks are more so. While it is true that non-AC defenses are lower they are not always lower and on the monsters you really want to hit (solos, leaders, brutes in your face) they often have at least one defense that is as good as AC or even better. Look at an Ogre Warhulk if you don't believe me.
The argument that warlocks also can attack a wide range of defenses also holds a little validity, but not as much as the designers would like. Here's the problem: a crappy roll always misses. Take the infernal warlock. He has two at wills that target reflex. He doesn't even have a choice in the matter so a clever player can't get around this. At low levels he has maybe one attack that can go after a different defense, possibly two. If he misses with those (remember players almost always have a 40%+ chance to miss) he is now out of luck and forced to go after Reflex or except making basic attacks with a weapon, where he can never match a rogue, ranger or defender for ass kicking.
Eldritch blast is in most ways a crappy long bow. It has: shorter range, No option for inaccurate long range, Does the same damage, is a wash for hitting as the long bow gets +2 to hit which mathematically means it hits just as often, and to top it off costs a precious at will power of which you can never get more. Every one either gets long bow to start or has to spend a feat at most. The long bow needs ammo which is a slight consolation, but it's not like arrows are gonna bust your character's budget.
So yeah at the moment the warlock is the crappiest of the strikers and if you are into balance not a good choice at all. You don't deal the damage of the other strikers nor do you have the options (feats) to match the weapon wielders yet. I hope that will change some when Arcane Power arrives.