There's always going to be a bottleneck in every system. Just because the 6700K can pair nicely with stronger cards, doesn't mean a 970 is a problem.
I didn't say "all games" 60+ FPS at 1080p, I said "some". You'll have to play around with settings to strike the best balance on any given title.
A 970 is still a relatively strong performer. I wouldn't buy one new, but if you have it already, it should be reasonable enough.