I believe 3D Touch is disabled by default on devices with 3D Touch. You may have re-enabled it in Accessibility...or you have Touch Duration set to Fast on one and Slow on the other. Or I could be wrong and Apple changed it so 3D Touch is enabled by default on those devices that support it, but it was certainly disabled by default during the Beta phases.

Regardless, it's still available as an option for phones with the 3D Touch hardware.