Am I wrong that passive flows, not earnings, are what's actually propping this market up?

Top 10 S&P names are about 41% of index weight now but only around a third of the index's earnings. Every payroll deduction into a 401k or target date fund buys that same top heavy basket no matter what the price is. Feels like real price discovery on the median stock has basically stopped mattering. Genuinely curious what people think breaks this. Does the passive bid just compound until valuations look insane by any historical measure, or is there some mechanism that forces a reversal before t