No, you're wrong. Index funds can and do track an index very closely. Index changes are announced months in advance and prices typically change very little on the actual change-over day.
Week 46 Wrap: Copper hits 2mth low as Trump threatens net zero pace; US rally fades; HotCopper’s picks
AN1 CuFe sells its Crossroads gold royalty to Northern Star for $4M cash; says better than waiting for mine launch