Yes, making a no brainer choice is bad design (at least, most times- there's a reason Tome of Battle was made, after all), but saying that sandstorm blast is more powerful than most eldritch essences is not necessarily indicative of this.
For one, there is still at least one comparable essence. Beshadowed blast, for example, can temporarily blind an opponent, which is pretty much a death sentence in low level combat. Now, you could probably still say 1d4 con damage is better than this, which is why I have lowered it down to 1, in admittance of this.
Even assuming Beshadowed Blast did not exist, however, there are other things to compare it against. Aren't all invocations supposed to be equal? Is a small amount of constitution damage really going to be the better option over 24 hour flight, charm monster, or at will invisibility? Such invocations can make or break encounters on their own, with proper use.
So yes, it may be better than most of the essences, but I don't think it makes it significantly more powerful than the other options that can be chosen for that level. Unfortunately, 3.5 does have its measure of imbalance, even among supposedly equal options (see toughness as compared to power attack- but I don't think anyone would argue that toughness should be the measure of a feat).
Despite my disagreement in the large though, I do appreciate your input, and think it is probably a wise idea to scale the essence back a bit, hence my edit.