some comments from my BF the Apple Store Genius
These were random idiots not the norm. Yes there are diags for the phone but outside of the battery and the wifi they can't determine physical issues. it is possible for both to be software based at times but not always
Because in general store managers have zero tech training or knowledge. So they defer to the actual folks in that role.
Okay here's the blunt truth. Apple Care doesn't control in store repair. They are not supposed to, by corporate instruction, ever tell a customer something will be swapped etc. And they certainly aren't supposed to tell you that an employee screwed up. The stores do modular repairs period. This is what they are told to do to by corporate. IF Apple Care wants to override that then that is there call and it comes directly from them. They have ZERO authority to demand or to tell a customer to demand a swap for a modular issue. Ever. And like it or not, when you bought the phone you agreed to certain terms of service which give Apple the right to determine the best course of action, not you. So you telling an In Store what they are or aren't going to do, especially the "Apple Care said and you have to do what they say" isn't going to get you anything other than perhaps an invitation to leave the store and never return. Especially if you were as mouthy and nasty in tone as your writing comes off