This isn't true, I had to use a 750 Ti when my 780 died and I could run GTAV on mostly high settings considering. Maybe had to turn one or two things down, and nothing was on absolute ultra, but still. I also played MGSV on high settings with it (I rushed out to get the 750 Ti in time for MGSV when my 780 died a week before release).
Either way, the 1060 is still the better choice, but don't underestimate the 750 Ti if you can get one very cheap.