My favorite DA limited for landscape photography is the DA 21. I'm very comfortable shooting at that focal length and can shoot all day with that one lens. Generally speaking, zooms are preferred in landscape photography simply because of FOV flexibility, which is more important in landscape work. When I go to iconic landscape locations, where you may run into dozens of other photographers, the vast majority (98%+) are using zooms. Most people building a landscape kit should start out with zooms, particularly a standard zoom and a telephoto zoom (DA 55-300 PLM is great for landscapes), and then add a few primes to cover one's most used focal lengths. I would also add that if a photographer who is shooting primes finds himself constantly swapping lenses, he's probably better off moving to zooms. If you're shooting primes, you work the focal length of the lens as long as possible. Often I would take my three limiteds (DA 15, DA 21 and DA 35) and end up shooting only one of these lenses all day. If I were going someplace where I needed quick access to a variety of FOVs, I would take a zoom.
Can you get better images out of the DA limiteds than primes? In my experience, yes. And it's not really an issue of sharpness. The DA limiteds are hardly perfect in that respect. My DA 12-24 is sharper toward the edges than my DA 15, but images from the DA 15 just look better, particularly in prints. Better local contrast, better color, more natural rendering of detail, better handling of flare, especially veiling flare. Prints from that lens generally have more aesthetic impact than what I get out of zooms. By using the DA 15, DA 21, and DA 35 Limiteds on my K-5ii and KP, I was able to make aesthetically more pleasing images than other local photographers who were using professional Nikon and Canon zoom glass on FF cameras. I wasn't capturing as much detail as these FF shooters (for obvious reasons). But there's more to image quality than the amount of detail captured.
Some images with the DA 21: