In a debate to discover the truth in a complex environment, who should win an argument?

The person who truly understands all of the arguments advanced by others.

A lot of debate is framed to the other person as "here's a thing you don't yet understand".

But sometimes the other party does understand it, they just see beyond what the debater sees, or on dimensions they aren't seeing.

In most situations we use the proxy of "person with formal authority" for "person best positioned to understand all of the relevant tradeoffs" but it's just a proxy.

If you're trying to convince someone else and you don't have formal authority, a winning move: steelman back the other person's perspective to demonstrate that you understand it, and still think a different thing is better.

The best indication that you understand an argument is the ability to steelman it (not just parrot it) to the satisfaction of one of its primary proponents.