It's my understanding that the designs of ARM cores are so inefficient that Apple doesn't use their designs and Qualcomm doesn't use their designs they just license the instruction sets. The last time Qualcomm used an ARM design it was a disaster (snapdragon 810 powerpig chipset). Q was caught off guard by 64-bit apple a7 CPU and in desperation used a 64-bit arm ip core, it was a total fail and overheated and failed in the marketplace.
So are we supposed to believe that ARM has fixed all of its mistakes now?
ARM has made the Cortex-X3 official today. With its up-to-25% performance boost over the X2, It will probably be a marquee core for next-gen flagship mobile SoCs; however, the OEM asserts that the equally new A715 and refreshed A510 have their places right alongside it thanks to their complementary power-efficiency and scalable specs.