The issue isn't it's usefulness in small transactions. The issue is who decides. In the case of gold a huge distributed system decides the valuation of Gold. Yes we usually use USD as the comparator. But there is a Gold:RealEstate ratio, Gold:Oil Ratio, Gold:Bread ratio. No single or small number of actors can change that in a meaningful/reliable way.[1] Whereas USD can, and has been, printed at an exponential rate.

[1] -(Let's exclude intentional market manipulations like if a world leader were to buy a bunch of gold and then saber rattle to drive up fear).