You are also talking max amperage capable of the connector, not the actual draw of the gpu in question. The gtx1070ti has a reference draw max of 180w, that's upto 90w on slot and upto 180w on 8pin pcie, so it's not going to exceed what a chain is capable of. The 75/150w rule is not much more than the safety line, kind of like the 70°C rule for a cpu or 80°C for a gpu, regardless if they are generally good for upto @100°C.
A single 6+2pin on a chain will be fine with a 180w draw, it's good for a max closer to @210w. But granted, that's pushing it since it's relatively unknown just how much is pulled through the socket and how much is needed by the connector.
But figure it this way, even if separate cables were used, that's still a single 6+2pin connection, the exact same as a single 6+2pin on a daisy chained cable, you only need the one connector. If you physically cut off the additional connector on the chain, you'd have the exact same thing as a normal 6+2 single wire.