Apple says the GPU inside the A14 Bionic is 50% faster than the one in the A13.
Apple said no such thing. Apple claims a 30% GPU performance boost compared to the A12 generation. Furthermore, observed performance for the A14 in the iPhone and the iPad Air (4th Gen) looks different in some important respects. iPhone benchmark scores for multi-core/multi-threaded workloads and GPU workloads look more modest than those for the iPad Air. That might be explained by the power management logic in the A14 doing what it is meant to do - the improved passive cooling permitted by the larger tablet format/frame/skin probably also allows those elevated multi-threaded scores (at the cost of slightly elevated power consumption) without causing any run away thermal build up. Looking at the A14 GPU scores for the iPhone and the iPad Air, however, that are so sharply different, makes one wonder whether the GPU in the iPhone has been locked to a lower frequency.
I would put 60Hz in the positives. We know that 120Hz is unnecessary. It drains battery and reduced performance drastically. Some metrics show it drains the battery 35% faster. Many phones with 120Hz even let you turn it off and never to 60Hz. It makes sense to have 120Hz in monitors: (1) they are plugged into he wall where power is not an issues, and (2) GPU's are expandable on desktops. As for phones 120Hz does not make sense. It is just a temporary fad at best.