the s&p 500 vs equal weight spread just hit 13.8%. it's only been this wide twice before

Been tracking the gap between SPX (cap weighted) and RSP (equal weight) for about two years. Last week the trailing 12 month return spread widened to 13.8 percentage points in favor of cap weighted. That level has only been reached twice before in the modern era: March 2000 and November 2021. Both of those times, mega caps went on to significantly underperform over the next 18 months. Which, you know, doesn't prove anything on its own. But it got me curious enough to dig through the full history. Going back to 2001 I found six distinct periods where this gap exceeded 10 percentage points. In five of those six, RSP outperformed SPX over the following 24 months by an average of 14.3%. The lone exception was right before COVID, which was its own kind of black swan that scrambled everything. What actually made me take this more seriously was the earnings picture. I had MuleRun pull constituent level earnings and revenue growth across all 500 names going back to 2001, then spot checked the outputs against Bloomberg. The numbers lined up, so I kept going. The pattern that jumped out most clearly: the concentration premium tends to unwind fastest when top decile earnings growth decelerates relative to the median. And Q1 2026 is showing exactly that. Top 10 names posted 11.2% year over year growth, down from 22.4% a year ago. Meanwhile the median company posted 7.8%, up from 4.1%. So the gap is compressing from both directions at once. Now the immediate pushback is "this isn't 2000" and that's completely fair. Today's mega caps are genuinely profitable with massive free cash flow. Nobody with a straight face is comparing NVIDIA to Pets.com. But profitability alone doesn't save you from multiple compression when growth rates converge. Cisco was a legitimately excellent business in 2000. Still took 15 years to see that price again. The lesson from that era was never really about business quality. It was about what happens when the market prices in perfection and then perfection stops accelerating. Random tangent but this also connects to something that bugs me about how people talk about "passive" investing. If 38% of your index is concentrated in 10 names, up from about 27% just three years ago, you're functionally running a momentum strategy whether you signed up for it or not. That's been phenomenal for three years. But at what point does "I just buy the index" become a thesis that deserves the same scrutiny as any active bet? Anyway. I've shifted about 20% of my equity allocation from VOO into RSP and IVOO over the past month. Still majority cap weighted. Fully possible I end up underperforming if concentration keeps expanding. Last two times the gap was this extreme, RSP beat SPX by 18% and 11% respectively over the next two years. Combined with the earnings convergence it felt like enough to act on, but I realize I could be reading too much into historical patterns that may not repeat in a structurally different market. Could be wrong. Probably overthinking it. But 13.8% is 13.8%.