Training for a long/climb-intensive hike with a pack makes sense to me to strengthen your core, quads, etc. Isn't running with a pack, even at a restrained pace, pretty hard on your knees, etc? Is there not a better way to get similar training?
I'm sure a high volume of pack running could be not so good for you, depending on how sound your biomechanics are. Mine suck naturally, but I've been trying to improve my stride while recovering from the ankle surgery.
I've not found anything that works better for getting ready for a race where you'll be spending lots of time running with a potentially heavy-ish pack. For me it helps to get a few workouts in on the step mill before running? 23# is a little on the heavy side but I rarely/never do a 24-36 hour race with something that heavy, so anything I do carry should feel light. At least, that's the idea!