An argument can be made here that Buick is not really a luxury brand, but somewhere in between mainstream and luxury - a.k.a premium.
This car should compete with Acura TSX, Volvo S60 and perhaps the Passat and whatever MK? from Lincoln.
Definitely the interior of his car is richer, more luxurious than Sonata, Malibu, Camry, Accord, Fusion, etc.
The base model's engine is a let down indeed, no doubt about it, but the upcoming 2.0T should be fine even though it would still have lower power numbers than the Sonata 2.0L. Too much power on the FWD, particularly not very sophisticated platforms, is prone to significant torque steer anyway is it not? IIRC, the 2.0T will have more goodies like adjustable suspension, some fancier steering, upgraded brakes, etc. That model should differentiate even more this car from the mainstream.
Once the car is produced in Canada vs. Germany the price will probably drop as well.