A genius ! Not at all !
Actually, I only discover this because I totally forgot to boot Sierra with nv_disable=1 as I was used to with previous OS X versions !
So it was just by pure luck !
It has actually been that way for awhile. You can boot El Capitan with built-in support for assorted lower-end GT 7xx models so long as they are Kepler based.
Really, this confusion is just because of Nvidia's naming conventions. 7xx cards should all be the same family (Maxwell) for the sanity of consumers.