You completely don't understand the idea that the great companies are the ones who can figure out where the future is headed. And trust me, customers don't know that.
And you completely fail to understand that >4" screens isn't the future, it's the present.
The "innovator's dilemma" talks about what new ways you should go in that don't yet exist, because what people say they want is not always actually what they want.
But with larger phones, people have already shown what they want. Many of them not only said they wanted larger screens, but have gone out and bought them. In fact, they have bought them in numbers rivaling Apple's own!
There's no risk here, there's no ambiguity, there's no concern that people might not
actually want it. Samsung and others have been selling larger phones with great success lately.
The only potential pitfall would be that people mistakenly think they want the larger screens, and only buy it once, then revert back to smaller screens. However, if this were the case, there'd be evidence of that happening now, and there isn't. There's no shortage of people buying larger phones, then upgrading to another larger one when something newer catches their eye, and there's no shortage of people buying larger phones and waxing on and on about how happy they are with that size.
Ironically, if the "innovator's dilemma" applies at all, it applies to the people here saying they wouldn't want an iPhone Plus. After all, aren't they saying what they don't want, when many of them don't really know whether they do or not? Have they seen a larger iPhone? No. So how can they knowingly say they don't want it? Isn't that exactly the sort of problem the "innovator's dilemma" is meant to address?