Well, high resource costs are problematic in terms of weapons, since they're size 1 which means only a fraction of the resource cost is used. I believe 1/2.
So resource heavy they're not. I believe outside of bolt-throwers the highest cost is 25. Which is marginal compared to some other nations, especially once you also add in the production bonus inherent to Underkings.
Secondly, the elite units side-step the axe question completely because they use hammers or magic weapons. The heirarchy tends to be axes, hammers, magic weapons, if one could divide the dwarven units into groups by their level of eliteness (so I made up a word, so what?)
This whole problem arises from the axe and hammer problem. Axes are inferior, so everyone wonders, why use axes? If I improve the axes a bit, they'll be even more similar to hammers, so everyone wonders, why have both axes and hammers? If I improve axes a lot, everyone wonders, why use hammers?
Despite well thought out arguments presented thus far, I am still leaning for my original thinking (which is the easiest and cleanest solution), get rid of the hammer dwarf warrior, and so remove the side by side comparison and choice of axe and hammer.