What bothers me about this industry is that if you were to interview for an iOS position at a place like FB and suggest a KISS type solution, say using PONSOs for the data model, you would immediately be shown the door.
KISS - Keep it simple, stupid
PONSO - Plain ol NSObject
A more likely case to the one you're describing would be someone suggesting implementing a search box with an O(N) search through an array (and offering no alternatives), and then being shown out the door.
Technical interviews are all about understanding how you approach problems, what kinds of solutions you're comfortable with, and how flexible you can be in the face of the types of constraints we encounter in our day to day jobs. So yes, someone who only knows one solution, and a non-standrd one at that, isn't likely to do well. But someone who knows the "rules" (aka the standard patterns) and can make a well-reasoned argument for breaking them in a specific situation is exactly the kind of engineer I'm looking for.
The existence and popularity of libs like Realm is proof that not only is the community not married to the notion of Core Data, but there is a lot of noise being made in alternative data model layers.
If you are shown the door for suggesting a KISS solution and avoiding a buttload of dependencies and performance hits, consider it a bullet dodged, since odds are those people are terrible.
No wonder I'm terrible at interviews.