It is easy to pick a time period that matches your conclusions. Just playing around with BRK-A vs. the S&P 500 on Yahoo Finance, I can see that BRK-A outperformed the S&P for many time periods since 2002. 21% better total return since the begining of 2010, 15% better since the begining of 2012, etc.

However, the point is true that BRK-A has not been a significant over-achiever in the recent past compared to the S&P 500. However, rather than this being from Buffett "losing his touch", I believe it is more from the S&P 500 being in a speculative bubble. Buffett has always said that he is likely to underperform the benchmarks when the stock market is full of speculative fever, as it is these days with the Shiller P/E ratio the highest it has been since 2000.