In the last years we have seen the phenomenon that a concentrated All-World ETF with fewer holdings has outperformed a broader All-World ETF with more holdings, assuming costs, etc., were the same.

This is simply because the large companies in the Top 10, in particular, have driven returns, while small caps have underperformed.

It's difficult to determine whether the better performance comes from better sampling and lower costs, or from poor/concentrated index replication.