Spoiler: They don’t suck! Check out Austin Mann’s comprehensive overview:

PetaPixel notes,

Everything, from pano mode, to time-lapses, to video capability to the vastly improved autofocus was tested and in every regard the 6 and 6 Plus outperformed its predecessor noticeably. […]

When the 5S and 6 Plus are set one on top of the other and forced to shift focus from a rock to the water it’s thrown in, the 6 Plus is lightning quick while the 5S actually never refocuses at all.

[YouTube]