Getting better fuel mileage than a ecoboost doesn't really say much. I know a lot of guys that complain about the EB's fuel mileage.
I bet they average about 17 as well!
I work with a guy who has an Ecoboost, and he is averaging 15-17 mpg in most driving. He says the best he ever got was 21 running 60 with a tailwind. It's a totally stock ECSB 4x4, so it's not like he is running mods that would kill the mpg.
He is so happy with the mileage that he parked the truck and bought a Cruze to run around in.
The new powertrain lineup in the GM models does look promising, but I am still not fond of the styling.