That's absolutely absurd. Large screens aren't "just a gimmick". It's just about the most non-gimmicky thing about phone hardware. A bigger screen is always better from a presentation and UI flexibility perspective. However, increasing screen size affects portability and manual usability. There needs to be a balance between the two.
iOS was not initially designed for third-party apps (lack of foresight), the SDK was released for its initial, resolution-locked model (lack of foresight), and now Apple is stuck with losing the backwards compatibility of its entire app ecosystem.
Turns out Forstall's screwups are systemic and not just limited to Maps and Siri and skeuomorphism.