I'm afraid that the success of Medfield and its follow-ons could be something that simply is not related to performance or performance per watt or whatever. From the point that Medfield is simply usable or at least in the same ballpark with ARM offerings then it is marketing, carriers and design tricks that will do the job (or not) for Intel.

We are talking here in a tech savvy forum. But people who actually buy phones, know nothing about ARM, TI, Tegra whatever. They know Apple, Android (probably), Verizon, things like that. Most probably they have heard Intel, so a program like "Intel Inside" could work for them (what would the average user make of a "nVidia Inside" or even worse "TI inside"? ). People will probably buy the slick design phone (e.g. iPhone), or the one that is on offer by their carrier.

Intel just needs to be in the same ballpark with ARM. It doesn't need to have the highest performing device nor the lowest power consuming. After that it all comes to the marketing money it is willing to spend. And it has a lot more money than any of the other players.