Cadillac is trying to compete with German luxury cars primarily. That is a big change from attempting to be the best of the Detroit 3 luxury barges. It takes a lot of time to make a change like that. First they have to build vehicles that can compare favorably to Audi, BMW, and Mercedes Benz. Then they have to take buyers away from them. Moving into a different segment is difficult to do. I drove a CT-6 and it is a terrific car. Sizewise, it is between a midsize (E300) and full size (S550) and isn't as luxurious and the A8, 750i, or S550. The CTS already fits in the midsize market and Cadillac claims that a new full size car is on the way in a couple of years. If I wanted to spend $65,000 on a sedan, the CT-6 would definitely be on the list. Pricewise, its closer to the 5xx series or C300 when comparably equipped.
Buick is trying to compete with Lexus. They are on par with reliability, but they don't have a car that competes with the E350 in luxury. They top trim level of the LaCrosse is close to the base E350, But that is just the beginning of the E350 line. GM does have a ways to go in the luxury category.