The structural difference between funds and ETFs shows up most clearly in the tax bill, and it compounds over a long holding period.
Two portfolios can hold nearly identical assets and deliver different after-tax results. The difference often sits in the wrapper rather than the holdings.
ETFs generally distribute far fewer capital gains than comparable mutual funds because of how shares are created and redeemed. For a taxable account, that gap accumulates.
None of this makes the wrapper more important than the allocation. It makes it worth checking, particularly for the largest positions in a taxable account.