I opened an account here just because of how ridiculous this demand is.
First, I highly doubt that an update would damage your computer physically. Doing the BridgeOS recovery should resolve the issue. It was either not done or done improperly. I would also put serious questions marks on the store that confirmed that it was a hardware issue (if you actually visited one, you might be just assuming without a document saying that).
The fact that you used the computer only once or twice is totally irrelevant. Warranties start from the day you buy the machine, not the first time you used it. If you've got money to spend on a 3000 USD computer to only use it 1-2 times, that's great for you, but still irrelevant.
Considering that it's been several months since you bought it, that rules out any buyer's remorse refunds, so Apple's responsibility is to make sure the issue is resolved, regardless of its cause.
Apple is willing to service the machine, they are not denying you of anything. If Apple (or any other company) were to give out brand new devices upon first contact for every device that has issues, they would run out of business with the amount of people that would take advantage of that.
Also, if you talk to a lawyer, you'll most likely be shunned away. Manufacturers are not obligated to give you new devices just because you ask them to and especially in a case where it's almost impossible to prove that the update was what bricked the machine. (correlation does not equal causation).
Just let the store repair the Mac. At least don't be thick and stubborn and have the Mac repaired and sell it on to cut losses.
And don't be as defensive as you are being, it sounds like you have something to hide.
