You can see here how the S&P Smallcap 600 Index has slightly outperformed the Russell 2000 since the market lows in February. This could be due to how the indexes are constructed. Typically a company needs to have four consecutive quarters of positive earnings to be included in the 600 while the Russell doesn't have this requirement. The Russell 2000 Index consists of many companies that are losing money so theoretically it makes sense that it underperforms.
It is interesting to consider how many of these companies and other assets across the various financial markets are overinflated because to the ETF and 'Passive Investing' craze that is underway. How much demand for these assets is solely due to the fact that they are included in an Index which causes Index funds to have to own them? I think eventually the chickens will come home to roost and there will be a huge unwinding in the markets.