I think the 3 at the back was just an opportunity against a weaker opponent for Berhalter to maximize his scouting of the CBs he has available to him in this Cup. I think in a perfect world you have Brooks and Miazga as your primary CBs in your A-squad with Zimmerman and an additional guy as backup options. I also think the 4-2-3-1 is a more appropriate formation moving forward with much more talented CBs and fullbacks joining for WCQs.
Ideally, would love to see this for WCQs:
Steffen
Dest-Brooks-Miazga-Moore
Adams-McKennie
Musah-Reyna-Pulisic
Dike
And that leaves tons of depth options on the bench as well.