Is it not a sports car simply because it is so refined and well-mannered..?
Nothing wrong with the ST. To me, actually, that refinement is a selling point. It's quite comfortable and luxurious, notably quiet, especially for the price -- but you can still let it off the leash. One appeal of hot hatches is the "under the radar" quality, and the ST has that. The other hot hatch attraction is versatility. You can drive the ST hard, or take it easy, which is valuable to me since it'll be a daily driver, not a track car.
But people that want a more raw, rally-car kind of feel might not like that so much. It's one of those personal preferences.
Gas mileage is great for 250 hp (much better than the WRX; about the same as the GTI, despite the 25% advantage in power). Actual mileage is going to come down to how you drive it. But if mileage is your main concern, you shouldn't be looking at the ST, or even this segment. There's a Focus PZEV that breaks 40; try that one. Or the Fusion hybrid, at 43 MPG in a big family sedan. Plenty of room for that 5000 mile roadtrip.