Although it is not necessarily applicable for everyone, I think environmentally it makes a lot of sense to focus on using as much natural materials as possible and reduce embodied carbon in building materials even if it's at the expense of performance. Ultimately, this doesn't need to turn into some sort of competition of who can have the least energy input to heat (regardless of energy input to build). If we use wood heat, even if the house is not R100 walls, we are still using a renewable and eco friendly resource, and performance of the walls is less important. What will matter more in this case, is that the house was built from sustainably/locally harvested timber, with minimal imported/highly processed construction materials, whose embodied carbon has a huge impact on the overall environment effect of the house.