This is something I hear a lot and I just don't get. Are the people on the other side of those deals just...not greedy? After all, you are implying that the deal has better expected returns than what people are buying on margin in public markets, so why doesn't the person on the other side of the deal take a little more for themselves by selling there instead (at a slightly more favorable interest rate)?
Is it because the rich investors are needed to bring some level of expertise or connections to the investment to make it work? If that's the case, and it seems likely, I would not say they are getting "access to better deals" per se. More like they are getting a normal rate of return and they have a valuable asset that they are renting out as well (their expertise or connections), and it all gets rolled into one number. But complaining about the rich having valuable assets is different from complaining about them having access to better investment opportunities.