> I found S&P 500 Equal Weight to be pretty attractive.The rebalancing required to maintain equal weights means constantly selling your winners and buying more of your losers. That creates volatility drag. Stock returns are highly skewed: only about 4% of stocks outperform the market, and are responsible for most of its gains. By keeping your allocation to those stocks small through constant rebalancing, you are missing out on a large part of their gains. The vast majority of stocks underperform.
Maintaining the equal weighting also requires constant trading, which generally means higher fees. A market weighted fund, in contrast, naturally maintains its desired balance in response to price movements, without any trading.
Also, the equal weighting ignores the amount of outstanding float for each company. If the fact that NASDAQ has not (historically) been float-adjusted (a common anti-SpaceX talking point) gave you concern, this is even worse, due to the multiple orders of magnitude difference between the largest and smallest companies in the S&P. If enough money enters the equal-weight index, this can spark large amounts of buying in (relatively) small companies that is divorced from their economic performance.
The equal-weight index has outperformed the market-weighted index in some periods (not in recent memory), but with higher volatility (so worse risk-adjusted returns). That outperformance can mostly be explained by factor tilts implicit in the equal weighting (e.g., a higher allocation to mid-cap value stocks).
You would probably be better off with a mix of market-weighted funds explicitly designed to give you the factor tilts and risk exposure you want.