> Growth is a useless indicator. The whole point of Piketty's argument is that the return on capital tendentially outstrips the rate of growth

I'll sidestep that Piketty measures wealth and calls it capital. Because that observation says nothing about how risk is distributed across those returns.

> large investors have access to especially high return assets

$1bn doesn't make for a "large investor" in institutional terms.

> OP is right that a 5% average annual return is conservative

No, they are not.

There are objective measures for this. I've worked closely with endowments the world over. A manager pitching a 5% target return on a fund with a 3.5% annual drawdown as conservative would be fired. A banker pitching the same would be subject to professional sanctions.