Gorehowl was associated with not just Grom but Garrosh and was prominent throughout. Purely by being in the RTS and being associated with an RTS protagonist elevates Gorehowl, but even foregoing that and just going by game appearances, it took until Wrath for Varian to return with his sword (Which can split into sword making it more of a fury weapon anyway) whereas Gorehowl has been referenced even prior. To know Shalamayne's lore you need to read the atrocious comic book or wowpedia. To know about the axe of Cenarius you need to read the even more atrocious Knaak novels. Gorehowl on the other hand constantly pops up in pivotal moments and what gimmick it does have beyond just recognition, i.e feeding off of those it kills to get better at killing lends itself perfectly to gaining power the more you use it. Also killing a C'thraxx and killing a Pit Lord isn't too much of a rush and that Gorehowl being used to chop down tons of demons elevates it, it's iconic across mediums.
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Chance of Knaifu appearance rises.