The intensity of their fight was such that people looking at the mountain would see a storm at the top of it. They fell a ridiculous length into the water and both of them did not consider that an especially huge impairment to keep fighting. They chased and fought each other, without pause or rest, all the way up the mountain, from beneath it, which speaks to their endurance. "Cracked off a giant avalanche" would mean saying all he did was send snow and ice rolling along when it states "broke the mountain side" as far as his death throes.
It's certainly beyond going:
The text is pretty strongly leaning into that both threw a lot of power around.If we are talking Durin's Bane, well, it fought and fell really far and long with Gandalf. There was some lightning flashing about. It died.
I'll say it another way. If the two of them going at each other can generate what looks like a storm of intensity enough to obscure the mountaintop that it would have been visible to people who would have wanted to look at said mountain, I'm pretty cool with that the Balrog can be read to have smashed up that much of mountainside in its death throes.
It's one thing to go "the exact limits of that are hard to parse" it's another thing to go "so I'm going to lowball and talk about it as being barely impressive as hard as possible in ways the text itself does not bear out from its clear context."