In the example of the balsa, if you think about it, you need a whole bunch of weight to offset all that light wood. You end up with a fight between the weight wanting to control and sink the lure and the very light wood wanting to make the lure float. This wrestling match is what creates the lively lure.
In the case of the heavy wood, you need far less weight to make it sink so there isn't such a struggle between the more dense wood and smaller volume lead needed to make it sink and so you lose some of the action.
Nevertheless, it has been my experience that you can't assume this will always hold true. Find a lure shape and size you like then build the lure out of several woods and see what you like the best. You should also experiment with the placement of the lead, a small change in the location of the lead can make a huge difference in lure action.
You can put all the math you want into lure building and in the end you will still find it necessary to experiment.
Jed