Vote-value disparity and democracy

Courts in Japan have ruled a national election invalid because of vote-value disparity. Vote-value disparity is when the vote of one citizen in one place has a different weight than a vote of a citizen in another place.

It is difficult to have absolutely no disparity at all, but beyond a certain level it is considered a violation of basic democracy.

The equivalent of what has just occured in Japan, if I read it correctly, would be like a court in California declaring national elections invalid because those in states with low populations have a significant greater value to their votes for the US Senate.