How important is Tyvek/house wrap for a house with metal siding?
While I don't doubt that your father 'never installed a house wrap for a metal building in his life' I have to wonder how many of them were residences? Buildings with walls that trap moisture or where higher efficiency insulation is often needed? Bare and exposed insulation on the inside doesn't count.

Wrap is about what is INSIDE the wrap, not what is OUTSIDE the wrap. Tyvek lets moisture out while not letting air in or moisture in. Tar paper was the old school solution but it blocks air and moisture in both directions. Tyvek or other similar modern building is needed for insulated walls with poor circulation, metal or no metal.