In the short view you're right. But your assumption is only valid in a permanent downward trend. The fact is the market goes up over time. Thus, the best time to buy with dollar cost averaging is as the market is trending down, because history says it will recover.
No permanence is required. Dollar cost averaging makes sense only when two necessary conditions are met: (1) one is not good at calling tops or bottoms (in individual stocks or indices,) or is not advised by such a person, and (2) the trend over your investment time horizon is up.
"history says it will recover"
I agree it will recover. But that is not the issue. Saying that it will recover is nothing more than a statement that the country will not vanish off the face of the earth. The issue is: will it recover over most people's investment horizon?
History actually gives us very few independent data points on which to base faith in the vaunted "long term." Ten to twenty, at most. Not enough on which to bet the farm.
Strangely, people's confidence in trends over various timescales is inversely proportional to the amount of available data.