Creating iPhone6 and iPhone6+ designs by just up scaling iPhone5 designs

As we all know, iPhone 5, 6 and 6+ share the same aspect ratio.

Therefore, our designer just creates designs for various iPhone resolutions by just up scaling the design that he created for iPhone5 resolution to iPhone6 and iPhone6+ resolutions.

That leads to: 1. The font being scaled up as we move from 5 to 6+ (The content that a view(like a label) would hold remains the same across devices, as even though 6+ has bigger screen space, the text ends up occupying extra space as the font is larger)

  1. The spacing between the adjacent views being is just scaled up as we move from 5 to 6+

Basically, everything is the same, just bigger in 6 and 6+.

Not to mention, being a developer, coding such a design in the interface builder is not conventional(I get a feeling Apple didn't intend for thing to work in this way)

I watched a few Apple Design Interface videos and went through some of the documentation. It clearly mentions that the UI should be adaptive. That is, if there is a navigation bar, the back button remains 30*30 px on all devices (Not 30*30 on 5, 35.15*35.15 on 6 and 38.81*38.81 on 6+) and the Title Label just occupies the rest of the space.

I understand there are some exceptions like the landing screens, home screens (where it might be apt for the UI being just scaled)

Is this correct?

In spite of extensive searching I am not able to find credible resources which make the point I have mentioned above.