I like to say if your income is consistently growing at ~10% every year, when the economy is growing at 2-3%, you're likely making someone worse off. (Although that someone might be some billionaire in which case have at it).
That is like saying, "The average age of the country is growing at 0.1% per year while my age is growing at 4% per year, therefore I must be making someone else younger." Income usually increases over the course of a career, but in the end, people retire or die and stop contributing to the average.
Similarly, your hypothetical individual who 'makes someone worse off' must by definition be inheriting some scarce asset, be lucky, deceptive, coercive or inflicting negative externalities. Otherwise why would anyone trade with him?
This is not to say that inequality isn't a problem or greater redistribution would not be desirable. But you need to frame the problem correctly.
I know you're into finance. Are you familiar with the concept of a long-short hedge fund? If so, you should be comfortable with the idea of focusing on relative movement of two assets within an asset class, hedging against the absolute movement of the asset class as a whole.