I would not have thought to even look at this but for Arnott's comments. These comparisons could be very important for investors who use broad-cap size or style ETFs to build their portfolios. On the surface, PRF clearly looks like it is meant to capture, and enhance, large-cap stock exposure.
A more well-known example of this concept is the Rydex Equal Weight ETF (RSP), which has outperformed S&P Depositary Receipts (SPY) ever since RSP started trading. RSP is not a better fund, but it captures a different part of the market, a smaller part. Ever since the market peaked, small- and mid-cap stocks have soundly outperformed large-cap ones, so it makes sense that RSP has beaten SPY.
This notion appears to apply to PRF. Any look under the hood would reasonably lead you to think this is a large-cap product. But combining PRF with small-cap and mid-cap funds may result in less diversity and more overlap than intended.
An argument that says PRF is large-cap and not a proxy for something else is no doubt plausible, but PRF does quack like a smaller-cap product.