voo vs. voo/vxus - is voo higher risk, but higher reward?

opening a $400k brokerage. deciding between voo or voo/vxus. a lot of people recommend two or three funds, including international... but i've been running test numbers (https://testfol.io/?s=lCKpRn6Bv9x), and over a 20+ year period, it looks like voo by itself would win out. obviously we can't predict what happens in the future, but is the idea here that voo historically outperforms, but including the international helps lower the risk potential in case the s&p 500 crashes like it did in the ea