That's tautological. Is there any reason rooted in -- for example -- portfolio theory to believe such a strategy will outperform market cap weighting on a risk adjusted basis?
Sector weighting equally is based on diversification. Market cap weighting will tend to bet more on winners (the market cap is going up), concentrating your investment there.
Another way to think about it: market cap weighting is a momentum strategy. Equal across sectors is mean reversion.
In the broader topic of portfolio management, equal weighting will outperform cap weighting due to the small cap effect (read up on Fama-French three factor model). tldr: historically small caps outperform large caps.
In this case, the equal weighting is abstracted away by 1 layer - each ETF is already cap weighted, so you aren't getting the full effect of equal weighting. Instead, you're reallocating to the ETF that has underperformed relative to all others, so as already pointed out, you are betting on reversion rather than momentum.
The small cap effect has nothing to do with sectors.
If the sector is big because it has a lot of medium/small sized constituents you gain from this implementation because a cap weighted index would under allocate to these smaller names.
