If you acknowledge that the Elves were losing in a one-sided fight, then you're acknowledging the exact problem with that my criticism is aimed at.
Whatever else you're saying to try to spin your words around to imply they did more than just get wiped out by the Troll is pretty much delusion. 'Look, they didn't die. See, they're weren't useless after all!' No, the meaning of usefulness is relative to quality of their contribution to the fight, and it's pretty clear that they contributed nothing.
Even as a thought experiment, did you think Galadriel needed any of the Elves' help to handle the Snow Troll?