With how polished Apples AI on mobile was at launch compared to Gemini on Android at launch were it could not even do basics like timers I suspect Apple had it in the works for far longer and it would not have been a total surprise.
Also you are describing the situation at launch for new hardware, the software will evolve every year going forward and the requirements will likely increase every year. If I am buying a flagship phone right now I want it to last at least 3 years of updates, if not 5 years. The phone has to be able to cope with what is a very basic requirement that is enough RAM.
This isn’t some NPU thing, this is just basic common sense that more RAM is better for this, something the flagship iPhones could have benefited from for a while now.