I sense it's time we reinvigorated this topic. Thanks to Tiberius and a couple of comments from ModDB, it seems that the said ultimate spell is once again the talk of the town. The upcoming siege and spell revolution is to pave the way for a renewal of our discussion.
I wholeheartedly agree with the main argument: Dwarves do not bend and control the fury of nature with magic. They're formidable builders of grand cities and mines inside the heart of mountains. Master of colossal engineering. Such monumental machinery thus fits their lore and smithing soul more than anything else.
Besides, I was also thinking about another version of the proposal: what if the summoned hammer were permanent? I mean, as a sort of very offensive building that generates seismic waves once in a while. I know that some might question this, saying that two structures as ultimate (fourth tier) spells are too much, but isn't the very fact of utilising two enormous buildings as final features unique by itself?
We should not even forget that the Twilight Queen's earthquake ability has become an actual concept of ordinary games, as the eponymous spell shall unlock her sublime form without the One Ring. She casts those quakes with sorcery, and that's why there is no instrument needed. Having an ultimate spell that does the same thing would not feel right, methinks.