Can’t comment if the index is broken or is functioning as expected. The answer would be different based on what your time horizon is; pretty sure S&P 500 is highly up since the 1998 peak. It’s at 4500 compared to 1300~ at its peak in 1998.

It will be broken(temporarily) if Nvidia(or take your pick) starts crashing but you might still do better than betting on an individual stock.