Hm! I may be among the oldest on the forum, and among the newest to poly.
How about this: people who have worked at self-awareness and mindfulness will, in many cases, cope better with the ups and downs of relationships than those who are not so aware?
But this applies to all personal interactions, doesn't it? Such people are likely to cope better with co-workers, obnoxious teenagers, aging parents, etc. It's a little like saying, People who have worked at their driving skills are generally better drivers.
I think that in interpersonal matters such people are often natural leaders, though. They assert no authority but people like them, respect them, and tend to turn to them for opinions. That's a very different matter from people who appoint themselves spokespersons or who work their way into leadership positions in activism.