The most obvious first principle is that a better value system should keep you alive. Being alive is foundational.

From that you can derive other principles, like value systems should result in the production of food, clean water, protection against wild animals and invaders, disease, etc.

From that you can derive yet more principles, like the value of efficient resource allocation, stable governance and so on.

And judged by basic things like "is this set of cultural values good at keeping people alive and healthy" you can quickly conclude that some are better than others, objectively so.

To deny this is to argue that wishing to be alive rather than dead is merely an aesthetic preference - an absurd starting point, lacking any intellectual merit.