I think you know much more about the legendarium than I do, but I want to nitpick one point:
Also, there were no more than 3 or 7 balrogs ever according to later writings by Tolkien, which indicates that no balrog was weak or cowardly.
I think I should have phrased what I said differently. No balrog was weak or cowardly in an absolute sense. Durin’s Bane attacked and defeated all the dwarves of Khazad Dum at the height of their power. It wasn’t initially afraid of Gandalf. However, Ungoliant was another matter. She had consumed the light of the Two Trees and overcome Melkor himself. She might also have been capable of doing something far worse to a Maia than destroying its body and banishing its spirit. I think that though the balrogs were able to drive her away, their victory was not inevitable and I can imagine even a balrog faltering when called to face such a foe.
I think you know much more about the legendarium than I do, but I want to nitpick one point:
I think I should have phrased what I said differently. No balrog was weak or cowardly in an absolute sense. Durin’s Bane attacked and defeated all the dwarves of Khazad Dum at the height of their power. It wasn’t initially afraid of Gandalf. However, Ungoliant was another matter. She had consumed the light of the Two Trees and overcome Melkor himself. She might also have been capable of doing something far worse to a Maia than destroying its body and banishing its spirit. I think that though the balrogs were able to drive her away, their victory was not inevitable and I can imagine even a balrog faltering when called to face such a foe.