Lens quality varies with the lens.
The 24-70mm f/2.8 II beats Canons best primes at some focal lengths. Its a good first lens in the high end region, you will not have to worry about upgrading it soon.
However, when you stop your lens down, as most do for landscapes, a coke bottle might do just fine
While we all like fine lenses, and I have and use some of the pricey ones, the advantage tends to come at the wider apertures. But, for landscapes, you want depth of field, which sometimes means shooting at f/8, f/11, f/16 or even f/22. Its a waste of money to buy a expensive wide aperture lens when the image is limited by diffraction at the small apertures.
So, for landscape, the low cost consumer grade prime lenses will be wonderful at f/8, f/11/ f/16, as will expensive zooms and fast primes.