If we made a similar comparison to the SP500 index since its inception in 1926, and made a chart of total returns difference over 1 year sliding window, between

If we made a similar comparison to the SP500 index since its inception in 1926, and made a chart of total returns difference over 1 year sliding window, between index and index minus it's top 7 performing stocks, i bet we will see this recent period isn't at all exceptional. Every economic boom is propelled by one or two sectors that have a limited number of players.