From one perspective, per capita is fair, but from another perspective it isn’t. The Constitution actually did a reasonable job of trying to address both cases, it just didn’t adequately account for such a huge swing in population and technology. One could argue that that is a failing of the people that came afterwards, since the Constitution also provided mechanisms for modification.

For an example of where it is not fair, consider an agreement between three groups and we all agree to vote on decisions that affect all three of us, say ‘how things are taxed’ or how often elections are held. Each group gets a vote, and 2 out of 3 wins. If that’s the agreement we entered into, my group would expect to get a vote now or a hundred years in the future even if your group grows it shrinks, it’s an agreement at the group level. Especially if we made considerations for a different type of vote that does take group membership size into account. It would be pretty shitty for your group to get big and insist that it should make all the decisions for me.