Isn't Lars Kroijer more concerned about 2/20 fees, and active vs passive? If you're considering 3 passive index funds versus 1, what is wrong with that?
That assumes you have the same allocations as the overall world. Using "Vanguard Total World", I get: 56% U.S., 33% international developed, 11% emerging markets. If you can save on expense ratio by moving 56% into a passive index fund / ETF that covers the U.S. market, that's saving money.
I ignored an (American HSA) account for years, and finally split it. I went in the opposite direction you're wanting to go. I sold my total world ETF, and bought separate ETFs for US, developed, and emerging markets. But preference probably matters more, as in my case the savings add up to 1% over 27 years of compounding.