Morality has been getting better over time, right?

I don't understand the claim.

If you believe this, then in the comments below, please describe a scenario that could have happened, in which we would today believe that the values people had hundreds of years ago were superior to the values they have today.

It's not uncommon for societies to believe others more moral, particularly their ancestors, but not always. There is a whole noble savage genre. My first piece of evidence is that my society thinks it has improved on the past; I expect to find such a view less often among societies that are worse than their predecessors.

Ultimately, I don't care if my society would be approved of by (random tribe from a long time ago). It's still interesting that I can actually approve of their society more than mine, by my values!

If society agreed that another set of values were superior, they would adopt those values. In fact, they would already have those values, prior to agreeing.

Transition to a different societal structure is a game theory issue, not just a matter of agreeing about values.

In addition, the claim conflates levels. As an example, Laconophillia, extreme admiration of Sparta, is over two thousand years old. People have long valued valuing courage, discipline, more than they have valued valuing managerial skill, artistic ability, etc. They would take the blue pill, if they could, in order to actually value courage and discipline that much. That's part of valuing valuing those qualities. But they have no blue pill, so they go on valuing courage and discipline less than Spartans did, less than they would if they could.

Assuming the Spartans valued some things that they didn't value valuing (perhaps skill with a bow, or fine hair, or something), the Laconphile might now value valuing those things, while desiring to cease valuing those values - the person will not value valuing valuing the primary trait.

By losing track of the levels, you rendered the position you had begun arguing against artificially incoherent.