[Ibrîniðilpathânezel]

Rikae, I'm pretty much in your camp. The wings are referred both metaphorically and non-metaphorically, which is quite ambiguous. Long ago, I came up with my own rationale for this: Since balrogs are Maiar and, one presumes, originally incarnated themselves in ways they chose, it's possible that not all balrogs looked alike, and this particular one chose to manifest itself in a shape that had wings in order to make a more imposing and terrifying appearance to its foes. The wings, however, are clearly not functional; we are never told that the critter flew. It leaps out onto the bridge, it cannot fly up after falling into the chasm, there is no inference anywhere that it is at all capable of flight. But it could still have wings for show, to make itself look huge and looming and threatening, and thus strike fear into the hearts of its enemies and underlings.

Now, one does wonder if all balrogs looked alike, or if they actually did choose different forms...? Hmmm.....