Taking a quick look, I'm pretty certain this isn't true. Let's compare the Monk to the Wizard from levels 1 through 10. I am consistently seeing the Wizard having higher base damage and significantly more targets. Now, this doesn't count Flurry of Blows, which is a big damage boost - just like a Striker deserves. And the Monk does have one genuine advantage - they can't hit their allies. But in terms of how many people they can attack and the base damage of those attacks? The Wizard is easily ahead.
Level 1: The Monk gets a higher damage burst 1 At-Will, with Five Storms. The Wizard gets the highest damage Daily Burst 2 (Freezing Cloud, which attacks twice, outdamages Masterful Spiral), but Spinning Leopard can potentially yield more attacks in the right circumstances. Monk has no relevant multi-target encounter powers, compared to the Wizard's Blast 5 Burning Hands or Skewering Spikes (any three targets within 5 squares.)
Level 3: The Monk gets Eternal Mountain, a Burst 1 that knocks prone. The Wizard gets Fire Shroud, a Burst 3 for more damage (due to ongoing damage) or the lower damage Blast 5 Color Spray that dazes.
Level 5: The Monk gets One Hundred Leaves, a Blast 3 that pushes. It runs fleeing in terror from Grasp of the Grave, which is larger (a Burst 2) that dazes on a hit, does full damage on a miss, and sticks around doing automatic damage each turn. For sheer number of targets, Fireball brings a Burst 3, and for sheer damage output, Stinking Cloud is a Burst 2 which inflicts full-power automatic damage each round.
Level 7: The Monk has Fist of One Hundred Strikes, which can hit 2 enemies within reach for not much damage. The Wizard gets a Burst 3 Repelling sphere for less damage, or can be satisfied with a Burst 2 power for higher damage and automatic damage the following round (either via Corrosive Mist or Winter's Wrath).
Level 9 Daily: The Monk gets Crane Dance, another decent one, which gives multiple attacks that knock prone with the ability to shift in between each of them. Of course, Wall of Fire can hit largely the same spread of enemies for automatic damage, or one can simply unleash Ice Storm for equal damage and immobilized instead of prone.
The only powers that can really compare are Spinning Leopard and Crane Dance, and even they are up against tough competition. In general, though, the Wizard has the edge in damage and targets and conditions. More than that - the Monk doesn't really have reliable multi-target attacks. Only its dailies let it truly hit a decent number of enemies - otherwise, it is pretty much limited to Close Burst 1s. The Monk comes out on par with the Swordmage, basically - a similar sub-controller with reliable access to smaller-scale multitargeting.
And the damage... 3d8, 2d8, 2d6. I have no idea why you consider those staggering amounts of damage compared to others. It isn't terrible, but isn't anything amazing in terms of raw dice. It can't compare to wizard attacks that hit multiple times or deal automatic damage. Now, Flurry of Blows adds a pretty big kick - but it is supposed to, to let the Monk fulfill its striker role. They can certainly contribute against multiple foes, but they certainly aren't making controller attacks obselete.
I'm just not sure where you got the idea that controller attacks aren't that good. Keep in mind, other classes tend to have specific features that enhance what they do - marks, striker damage, healing words. Controllers are very much tied to their powers, and it typically shows - those powers are often exceptional, and let them perform quite well whenever they can bring their multitargeting powers into play.
