You have some great points there.

If A is nothing other than B, then A does not add anything to B. If morality is a function of multiple other phenomena or even a complex or simple function of one phenomenon, then it does work.

This does not address the question of why I should be committed to the other's preference. If morality is just what I prefer for myself, it is tautologous that I prefer what I prefer. If morality is that I should advance your preferences, then that is itself a valid preference of mine or a value that needs justifying.

If your argument is that there are two concepts that we did not realize were, in fact, identical, then we should abandon one. Once there was the morning star and the evening star. Today we just call it Venus.

I have no problem with the subjective.

Water has macro properties that we are familiar with. H2O does not automatically conjure up those properties. If "water" were to slowly slip out of use, I don't think there would be much harm. "H2O" would carry the connotations of wet.

The problem is that people assume that morality does more than preference does. It attempts to point to obligations that your preference places on me. To deny that it does this extra work is a value statement. If you just withdraw assent due to lack of evidence, you are skeptical of morality despite accepting preference.

Your last point is the one that loses me the most sleep. If there is no moral realism over and above preference, then how do we prevent society descending into a game of chicken (as it seems to do every now and then on the international level). You could claim that there is personal utility to all sides to agree to the rules of a game. The rules of the game are justified only by the plausibility of all sides agreeing to them.