I’d respectfully disagree.
If anything, Buick is a premium brand at the moment. However, most of the current lineup was rushed to market post-bankruptcy to fill in the gaps.
Internally, GM is hard at work in making Buick a true luxury brand to go head-to-head with Lexus. You will see the first real Buicks, rather then rush jobs, soon with the Envision and next-gen LaCrosse.
The thinking is that there are two primary forms of luxury: performance luxury and pure luxury.
Performance lux is done by BMW, Audi, Infiniti, and MB, while pure lux is Lexus. Drive a Lexus back-to-back with any of the performance lux brands and you’ll see the vastly different experience.
Buick is for the pure luxury side. Caddy is for performance.
Like I said, Buick is a premium brand right now with a strong objective to move up and become a luxury player.