Wait, since when has WATER been Cthulhu's weakness?
Also, according to Lovecraft, Cthulhu was waking up (minor avatar), and yeah, his head got 'sploded by a steamship. That puts his endurance so many orders of magnitude below an Endbringer's that it's comical.
The resulting soup then reformed, and Cthulhu thought about killing the men who attacked him... before going back to sleep. It was the equivalent of a man being poked in his sleep, then rolling over instead of getting up.
While I refuse to hypothesize the presence of fanon-wanked hyperverse-Cthulhu, our memorable octo-head is generally a planetary-level threat, whose awakening ends human minds planet-wide immediately. He's also multidimensional, so he's kinda an endbringer in his own right- impossible to kill by mortals, and his "mountain-sized" true form should be able to pick endbringers up... even if they can shred straight through him.
What I'm saying, however, isn't a statement that an Entity could or couldn't win against ANY of Cthulhu's various incarnations... merely that, while a (insert Cthulhu here) vs (Insert Earth Bet Abomination here) battle royale could be interesting, a canonically-accurate Cthulhu waking up ends humanity's participation in this story, and Taylor running into him could break her brain. Thus, I very much doubt Taylor will run into him, OR ANYTHING LIKE HIM, in the caverns... at least directly. And while she may run into multiple hostile minions, powerful enough to be a danger to her, her current kit is at the top-tier of Mythos Minions, and she's clever. She might find challenges, but no serious "oh, SHI..." moments.
Basically, I was taking Brimstone's "SOMETHING is up" as a statement of worry, so I could contribute and keep this thread going, as I recall from my own meagre experience just how difficult it is to post something on a dead thread, and I really like this story.
Sorry about that. But, also- Seriously, when has WATER been CTHULHU'S WEAKNESS!?!? I know he can control fire, but SERIOUSLY?!?