Typically, after years of adding mulch and woodchips, which are both considered organic matter, soil texture becomes more friable and drainage improves. This is pretty much SOP for improving a heavy, dense soil. So I am confused why you now think this soil is some how deficient in some way.

Have you tested for drainage? That might be your first move, although raised beds almost always have superior drainage compared to unelevated planting areas. The second would be add more organic matter in the form of compost, but if the trees are already planted in this bed, adding any additional material becomes problematic.

As I said, I might be over-thinking this. When I put my Corillium in the bed a year or so ago, I asked at that point if I needed to amend. It's just that the soil is SO thick, dark, dense, and moist.
Other than the deer damage, they're pretty happy trees! :)

Thanks for the reassurance.