Adjusted Percent Return of BRK.B vs SPY

I read an article a few weeks ago stating that SPY has been outperforming BRK.B over the last 8 years.  Recently my friend asked me to check up on this so I looked into the data and it shows the opposite. 

BRK.B and SPY are both in the large cap space.  BRK.B is less diversified so it should have some outperformance, however it is also so large that it is also unlikely to consistently generate the return it has since the 1960s.

Here is a chart comparing the adjusted percentage return of BRK.B to SPY.  Since 2001, BRK.B has significantly outperformed SPY at a 330% gain compared to 190% gain.  Since 2010, however, the returns have been almost similar 194% vs 176% with BRK.B still outperforming.  Given that dividends would be taxed on the SPY re-investment, there is probably additional out-performance in owning BRK.B over SPY.