Idioms, how do they work?
Correct and appropriate.
Additionally No shit Sherlock ==> "You are stating the obvious"
which according to Wiktionary breaks down into
no shit (“an expression of amazement”) + Sherlock (“a fictional detective who makes ingenious deductions”)
As was already mentioned, no shit does in fact mean yes, exactly.
What is even better it's how you successfully managed to have the words no shit actually mean yes, a lot of shit. Whether you intended such a clever play on words or not you are indeed correct. I shit you not.