[obloquy]

Ecthelion and Glorfindel were two of the mightiest elf-lords of the time, and Gandalf was the most powerful force in Middle-earth, save Sauron, at the time of his encounter with Durin's Bane. A duel between two powerhouses is different than general combat. I think it's probably safe to say that the majority of the Elven armies were nowhere near Ecthelion's and Glorfindel's prowess in battle. Not to mention all three (Ecthelion, Glorfindel, Gandalf) were slain at their confrontations, and Gothmog's death was almost accidental. Let us also never forget about Orcs, Trolls, Dragons, and, in my hypothetical revision, the Boldogs. If Morgoth had an army of tens of thousands -- maybe hundreds of thousands -- of Orcs, and Trolls, with Boldogs intermixed as leaders and chieftains; and Dragons, some lesser, some greater, I can most definitely see a host of fifty Balrogs throwing everything in Morgoth's favor -- if it wasn't already. The later Balrogs were the greatest of Morgoth's servants. Quoth Legolas:

'It was a Balrog of Morgoth,...of all elf-banes the most deadly, save the One who sits in the Dark Tower.'

I don't think the kind of being we encounter in Moria is the kind you find in large numbers, and I believe that was Tolkien's intention with the note containing the tentative concept of 'no more than 3 or at most 7'. I contend that the note reflects the logical progression -- though it was never implemented -- of the Balrog's evolution. They started out in large numbers and weak, and were later developed into such powerful creatures that we should not suppose any more than '3 or 7 ever existed'.