Ok, I wasn't aware of the difference. I think the choice of name is confusing at best and purposefully deceptive at worst.
In that case, why not just use triple-buffering? And don't say it adds input lag. If done properly it doesn't add input lag.. and you don't have to worry about screen tearing.
Triple buffering still doesn't allow free flowing framerates, you just have more points it cuts off to when you cannot keep up the max framerate. Also the framerates it cuts to are not necessarily perfectly in sync with the screen refresh rate, meaning each frame is visible in different length of time which causes slight judder to the motion. This was a common problem in movies where the videos are 24fps and the screens were 60hz, they do not divide evenly. This is what Gsync/Freesync tries to fix, the monitor refresh rate changes together with the game. Even low framerates can look relatively smooth since there is no visible judder between frames.