@maxdancona,
You are focusing on a definition of "thrive" which I am not using. I am using "thrive" in the Eudaimon sense, not in the sense of growing bigger or more numerous or overpowering the competition.
Basically, I am arguing for a form of Aristotelian Virtue Ethics. This consists in pursuing what makes your life a "complete" life, in the ancient Greek sense of being autonomous, fulfilled, of our lives having been a "good project". Success is living life well, using our limited time and resources in ways that are productive, purposeful, important (to us), and satisfying, doing interesting, creative, relevant and helpful work for ourselves and for others, having friends and being a good friend, and (very important) helping others achieve similar success in their lives.
Aristotle described the eudaimon life life is one of “virtuous activity in accordance with reason”, and Epicurus described it similarly - having pleasurable experiences, good friends, and a meaningful, philosophical life. For Epicurus, "pleasure" was not purely self-indulgent (though, technically, he was a hedonist), rather it involved living modestly, gaining knowledge of how the world works, and learning the limits of one's desires. A life spent in this way would lead one to attain a state of tranquility (ataraxia) and freedom from fear. He said, "It is impossible to live a pleasant life without living wisely and well and justly. And it is impossible to live wisely and well and justly without living a pleasant life."
Obviously this won't work in all situations - no single moral system is free of corner cases where they don't make sense and, in fact, can be made to look ridiculous. But, combined with a judicious amount of Utilitarianism when it comes to social welfare, and the occasion appeal to Deontology when it comes to simply preserving stability and avoiding chaos, I find Virtue Ethics to be the most versatile, best fit for most situations.