Whether Nvidia did it by accident or design, the 970 was a good move. Having a card be so relatively close in performance to the top end, but at a budget price drove sales. Yes, it probably reduced sales of the 980 a little bit, but that market is different anyway - it is for those that want the best performance with no compromises, and are willing to pay for it.
Having the 1070 be a step back from that seems like a mistake to me. It is still a good card, but it isn't such amazing value anymore - its just another in a line of slightly better performance for slightly more money. Maybe they want to push people onto the 1080 but I think that could backfire because the kinds of people in the market for a 970/1070 are not likely to spend another $300 for a bit more performance.