Equal weighting removes the concentration of market-cap-weighting, but it is not free. Because prices drift apart, the fund must sell winners and buy losers at each rebalance to restore equal weights, which creates turnover, trading costs, and a systematic small-cap and value tilt.
The relative performance of an equal-weight version against its cap-weighted parent is a widely watched gauge of how narrow a rally is.
Example: in a 500-stock equal-weight index every name is 0.2%. The largest company, 7% of the cap-weighted version, has 1/35th of that influence, so a 30% fall in it costs the equal-weight index 0.06% instead of 2.1%.
Related: market-cap-weighting, free-float-weighting, index-rebalance, tracking-error, expense-ratio