It didn't have to try to "be the dark knight". It had to try to be a well done Captain America/Steve Rogers movie. For me, it absolutely succeeded. The broader themes of freedom and preemptive strikes were used to define who Steve Rogers is and his importance to the twenty-first century, IMO. It didn't need to go any deeper than that in regards to the poltical issues to make it a great film experience.
I know there's a need to compare every CBM to TDK or The Avengers, but Marvel's doing something different, I think.