> Gruber et al estimate permits are 50% of an LA home's price

That is not what Gruber shows. The 50% figure is that there's a permit adds a 50% premium on the value of raw land. In other words, the permit cost is "only" 33% of the cost of the permitted raw land. That's significant and a big problem, but very very far from "50% of on LA home's price."

But yeah structurally the solution is indeed to reduce the cost of production. Which if your 50% figure was correct, would be huge. But it's not correct.