When I pull this loaf fresh from the oven, it does have a hearty crust, but I can cut through it pretty well. Any day after that, though, it does take some effort, haha! I think it is just the nature of baking sourdough at these high temperatures.

I make a whole-wheat sourdough challah that has a lot of enrichment (oil, honey, etc) and is baked at a lower temperature (350) and I find that the crust stays much softer.