If pressed, you could put both the War on Drugs and the National on a Mt. Rushmore of the best indie-rock bands in the past fifteen years. But it’s more fitting to think of these bands — who will co-headline Fiddler’s Green on Saturday, September 28, for their Zen Diagram tour — as two actual mountains, 14ers even, distinct in their silhouettes but sharing the same rare, thin air above the rest of the range…