Consider an all-cap ETF like [VCN](https://www.vanguard.ca/en/product/etf/equity/9561/vanguard-ftse-canada-all-cap-index-etf), which is effectively strongly weighted in favor of large-cap stocks (around 80% large, 10% mid, 2% small).
From a capitalization diversification perspective, is investing in such an all-cap ETF still *significantly* better than just investing in a large-cap ETF?
Also, suppose mid-caps and small-caps come to increasingly outperform large-caps. Would the split among the caps in a typical all-cap fund then be allowed to freely change, would it get rebalanced back to roughly the current proportions, or would it adjust in some other way?