Not really. Look at London. Its primary focus of most its lines are to pass through the core of London. It is aided though by a massive amount of connections and interchanges that allow immense flexibility. Between the multiple lines with connections at key points, the Overground, the Elizabeth Line, DLR and a robust bus network, a problem on one line doesn't criple the network.

Adding a 4th trunk line (and more in the future even) through DC with more connections and transfer opportunities would do more to improve Metro service than express tracks ever could. Express service only really makes sense when you have the density for it. DC is not dense enough (and probably never will be) to justify the cost of adding express tracks and services on the Metro lines.