If I was you, and had a similar budget I would go with a GTX 1070, and then get an i5-4690, or try to get my hands on an i7 4790. Just make sure your board can handle those CPUs if you decide to go that route, and if you can even get your money back for the 1080.
To answer your original question: No. Why you got that 1080 instead of a CPU and GPU upgrade is beyond me, but I would highly suggest trying my idea. I am 99% sure the 1070 should max Watch Dogs 2, if not on launch day, it should after a few driver updates and patches. While I can't be completely correct, I just can't foresee this game running that much worse than other modern open world games that I can play on my currently laptop (i7 6700HQ and GTX 1070).