Saying it’s more efficient was meant to be a little tongue in cheek. It’s not now. It was a few hundred years ago when communication was still done by horseback.
Having local governments does mitigate the effect megacities have on rural locations, yes, but not regarding national elections. An argument I’ve heard time and time again for keeping the EC is that without it, each president would be decided by NYC and LA.
They covered this in Hitchhiker’s Guide. The answer is a towel. A towel is just about the most massively useful thing an interstellar hitchhiker can carry.