The argument is logical, but it is also a strategic dead end. The United States is and in almost any plausible scenario will continue to be a federal republic. We are constituted as a nation of states, not as a single unitary community, a fact that is hard-wired into our constitutional structure. Liberals may not like this, just as a man standing outside in a rainstorm does not like the fact he is getting soaked. But instead of cursing the rain, it makes a lot more sense for him to find an umbrella.
Liberals need to adjust their political strategy and ideological ambitions to the country and political system we actually have, and make the most of it, rather than cursing that which they cannot change.
There are certainly some profound democratic deficits built into our federal constitution. Even federal systems like Germany, Australia and Canada do not have the same degree of representative inequality that the Electoral College and Senate generate between a citizen living in California versus one living in Wyoming.
There is also next to nothing we can do about it. The same system that generates this pattern of representative inequality also means that — short of violent revolution — the beneficiaries of our federal system will not allow for it to be changed, except at the margins.