Yes, the simplest version of marriage is a social contract, but even at that level, there are commitments made, enforced by families, which leads to warring families in the case of breach.

There you go.

Hardly a model one should hold up as exemplary, worthy of returning to, and therefore irrelevant.

Your use of the term "therefore" implies that you are trying to use a logical argument, when in fact you didn't. The conclusion of "irrelevant" does not follow from your claim of "not worthy of returning to". It is relevant since it is in effect today along with the legal contract, so there is nothing to "return to".