It's "disproportionate" in the opposite direction (unfair to small states) if you consider small states as equally sovereign to big ones. Population isn't all that matters.
The top counterargument is, "Population is indeed what does matter in a democracy, other than some safety measures (i.e. Senate apportionment) to prevent the worst abuses of the majority."
OTOH the SC has five permanent members; even if we want to treat US states as sovereign nations there is no necessity to give them equal control over policy.