With 1000+ pages of LotR, I have a hard time believing this is the best joke Randall could have made. Or even an above average one. If you disagree, can I remind you: the joke is they were stuck in a hole. Because you know, if you are stuck in a hole with all your hole digging equipment, and the whole place is made of stone, why can't you carve some stairs in the walls of your hole? Like, carve hand and foot holds and climb out?
But I digress. What I was trying to say was, this doesn't strike me as the end result of "what's a funny joke about lord of the rings?" so much as the end result of "I'm going to turn to a random page in lord of the rings and try to make the best joke I can out of whatever I find there." And who knows, maybe this is the best joke that can be made out of the Dwarves unleashing the Balrog or whatever (maybe not, but let's pretend). In that case, the solution isn't to say "hey, this is the best I can do with this incredibly specific topic, sweet, let's post it" but to say "Well if this is the best I am going to get out of this particular lotr passage, I should really try a few more passages and see if they lead to anything better."
It feels, to take a new tack, like a Mystery Science theater 3000 joke. Read the first three panels in your best Ian McKellen voice, then switch to your best Tom Servo voice and add "So deep they were stuck in the hole, forever. The end, kids!" Mike (mike rules!) and Crow laugh quickly and the movie moves on, and you forget the mediocre joke because while watching it you also hear 400 other jokes making fun of it. This one doesn't stand out, but it's better than nothing, the only other choice the mst3k people have. Randall has more choice: if a joke isn't great, just keep writing until one is better. And if you can't think of any good jokes, get out of the webcomic business.