It was a very poor decision to add VOO to the asset list in Z9 system, for two reasons:

1) It is in perfect correlation with XLI so it does not bring anything new to the table in terms of diversification.
2) Its data starts in 2010, pushing the backtest entirely into our most recent bullysh period. But who cares about investing strategy performance tests during a time of record growth?

A much better change would have been to keep the old asset selection with data starting in 2007 and showing how the Z9 system performs at the end of the last big market crash. Would have been much more convincing that the strategy works well! Or, maybe this was done on purpose to hide some weaknesses of Z9 and people need to be scared of using it as a consequence?