In the South, yes -- air conditioners are definitely the biggest cost we have for electricity.
I do feel that hempcrete would be a good building choice for a lot of places in the US, based on insulation capacity and relatively low cost of materials.
But the cost of labor to build with it would be higher, due to lack of familiarity with the materials, and it would take longer to build with -- especially compared to prefab or other higher speed building methods. And then there's the increased cost in labor to do the interior fittings.
I am a fan of hempcrete. But it will take significant adjustments to the building process here in the US.
Hempcrete is not only for winter months and keeping heat inside. It's also very good for keeping the heat outside of the building in summer.
[https://www.youtube.com/watch?v=_5lDwBiQNc0 - Israel, no need for air conditioner, hempcrete keeps inside temperature between 20-25C all year round]