When they came out with a 1060 it was a replacement for a 960 in the series even though it performs way better. Each generation shifts every # higher in performance. A 1060 can actually do proper 1080p ultra gaming but previous -60 cards cannot without sacrificing serious frame rate or settings. That doesn't mean the 1060 is magically now a 970 replacement just because that's its closest previous generation card.
Ultimately this is a semantics argument. Defining what it "replaces" depends on what exactly you mean. If you want to define it as "whatever is closest from last gen" then go for it, but NOBODY else uses that definition. Nobody says a 1060 replaces a 970. They're very close in performance, so nothing is being "replaced." On the other hand, a 1060 does replace a 960 due to its place in the hierarchy, combined with pricing and an improvement in performance.