You are one of the few good traders on ET. My brain is old and especially tired today. Could you possibly explain this in a way an old, tired brain can grasp.1. It is almost certain that (literally) "all" investors invest in index funds. However, the more people investing in index funds leads to opportunities to buy the winners and short the losers.
2. Too hard to tell. There's nothing from stopping people from buying SPY and shorting 1 or 2 losers (in appropriate weights) on Monday, even if "only" 5% people are indexing. The number of people indexing doesn't need to be very high to create opportunities.
.