Hmmm...
As I'm looking through at the monk, I wonder how much they value Deflect Missile.
I know that its probably too situational that anyone would assume it doesn't see play, but what does WOTC see it as?
If I make the very generous assumption that it comes up every round of combat, yeah, it reduces damage by a minimum of 7 damage, maximum of 16 damage (assuming +3 dex) at level 3.
Let's also make the generous assumption that the player will, rather than spend the Ki on Flurry of Blows, will spend the Ki on Deflect Missile's second effect. That would be an extra 2d6 damage to an enemy.
Now, I would say this is actually decent, except that its 100% dependent on the dex save or else it ends up doing no damage, which means its less reliable than flurry. But I wonder if they make the assumption that the enemy will fail regardless.
If we did that, then the average damage the monk deals out with Ki is 1d6+3+1d4+1d6+3+2d6 = 22.5 damage at level 3.
And the momk mitigates an average of 11.5 damage, effectively adding your entire HP pool for every two turns you use deflect missile, without any Ki.
So maybe WoTC overvalues Deflect Missile? They think monks constantly use that feature and therefore keeps up with other martials in their own way?