You're assuming that the German flag was an imposition by the Allies, but actually it was chosen independently by Germans in both the east and the west.

The flag introduced during the Allied occupation wasn't the black-red-gold tricolour but something called the C-Pennant: a swallow-tailed flag with five horizontal stripes, blue-white-red-white-blue. This was only a provisional civil ensign for German ships. It was not a national flag, and it was very explicitly not supposed to be treated like one.

As the two new German governments took shape they each had a debate on their national symbols. It was clear early on that the West was going to have a black-red-gold flag, as those colours were traditionally associated with republicanism and a more liberal nationalism, but the tricolour was only one option. The other major proposal was the Resistance flag, a Scandinavian cross style design created in 1944 by a resistance member named Josef Wirmer. This design was championed by the CDU -- who even went so far as to use it for the basis of their party flag -- but in the end the the West Germans wanted to emphasize their state as a legitimate successor to the Weimar Republic.

The East, oddly enough, was originally going to use the old black-white-red flag, which had been the colours of the anti-fascist National Committee for a Free Germany. It was adopted as a kind of compromise design at the Second German People's Congress in 1948. The Soviets would have preferred a red flag but the Germans weren't really keen on it. In the end the black-red-gold flag was deemed a more appropriately revolutionary symbol than the conservative imperial flag, and it was readopted at the Third People's Congress in 1949.

In neither case was failure or impotence the main connotation of the flag. Rather it was seen as emblematic of certain political traditions in German history.