Ha! Might be a sign that none of us really have a firm picture of balrogs in battle, other than "big and scary".oh dear we're again so far away from balrogs...
The crudeness, in my mind, isn't because of any lack of skill, per say, but lack of care. They don't need fancy-smancy weapons to bash someone's skull in -- that's for weaklings like Sauron!i'm not sure about this...
they are maiar and fire spirits and morgoth would have sophisticated smithies at angband.he probably was able to corrupt a few more of aules servants than just sauron...
so why would the balrogs wield crude weapons? in fact i think their weapons should be exceptionally well made!
but i like the design of the club and the sickle!
Perhaps trolls wield something like your average club (doesn't require much thought to use) or we use ideas like the troll with flails on the stumps of its arms from Battle of Five Armies.
My point is that the Balrogs should be beings not of this world. I used trolls as an example of beings that, while fantastic, are alive because of a biological system like the one humans and elves have. They are children of Iluvatar. Balrogs are supernatural entities of shadow and fire. Their fall have constrained them and limited their power to change shape and create things at all and they have become purely destructive.
So maybe they create their weapons in the way we said Eönwë does, and they do it when attacking the Lamps. Their last act of creation is the expression of anger to shape shining, burning swords, whips and whatever, which then remain their weapons but just like them turn to shadowy, burning and deformed things.