While this may be true for high fidelity gaming, for moving some textured triangles around, mobile GPUs are fine. Also, they can (and do) perform much better clock-for-clock vs a PC (and especially a Mac) thanks to the ability to optimize drivers. For a fascinating discussion of the optimizations possible, Carmack's 2014 Oculus Connect keynote is well worth watching: https://www.youtube.com/watch?v=gn8m5d74fk8

This talk was a slightly long but very informative discussion of the various challenges in reducing latency and dealing w/ PC rendering: https://www.youtube.com/watch?v=PoqV112Pwrs