You're all correct in that Student Company Loans debt is cheap and maybe best not «over paid» if risk free investments can outperform the interest rate. (underthemoneytree.com)
But stripping all that away, I think it's more fair to compare them to other risk free investments than it is to compare to stock market returns. (allfinancialmatters.com)
First, there could be more sizeable changes in the equity risk premium (the amount by which stocks are priced to beat risk free investments). (hussman.net)