Fair enough - if you have the budget/ or have someone else paying to support purchasing separate 5.5" and a 7.9" devices. But, if you are in a position buy only one device - comparisons are involuntary. And Apple is clearly pointing out what they think is the right option.
And...
Apple are clearly painting a picture of the OSX/iOS a ecosystem as a continuum, across devices, regardless of device.
It even has a name - Continuity.
Of course each device is different, with different features, but they are def converging, in style, in features, in appearance, in specification, in user-interface.
Even on this forum, new rumours have posters guessing names, such as ipad Pro, thinking that the naming conventions of pro/air/mini across the devices. It rarely happens like that though.
And, the pricing doesn't quite fit the idea of there being a single iOS device, at 10 different sizes.
So, who knows...