electricity is very expensive where i live... That's why i use nvidia for mining.
I guess this chart is for Ethereum. This is only algo in witch AMD and 1070 are better than 1080 or 1080Ti.
i don't mine Ethereum.
For other algo, hash/watt is similar for all nvidia cards.
But to get the same hash rate for rig with 6x1080Ti... you need 10X1070... this means two rigs, so you have to buy second MBO, CPU, PSU,...
But if you plan to mine Ethereum, 1070 or Vega is the way to go