It's not about rushing and cramming as many features as possible; it's about introducing new useful features that work seamlessly in a new phone.
When I was an intern in 2004, I was a supporting role in a TD department in car electronics company. The project was about implementing car camera. The clarity that was achieved then is already as clear as what we see today. Many TD companies have a lot of projects on hand and are way more advanced than what we see in market today. So don't be surprised how many advanced stuffs apple and other companies are doing now.
As for seamlessly.. When Apple introduced large iPhone 6 and 6 plus, they also introduce a feature known as Reachability.. To double tap the home button to lower the screen to half so that the thumb can reach the top of the lowered screen.. It works even when inside an app. Sure.. Android has apps like one hand mode for Xposed mod on rooted device but nowhere it works as seamlessly as iPhone.