There is only one camera position from which you can frame any shot exactly the way you want it using a prime lens. Any closer and you crop out part of the image and any farther away and you need to crop the image you have captured.
If you are in that serendipitous position every time, a prime is great. However, when shooting landscapes, zooming with your feet is often difficult or impossible.
That is where a zoom comes in handy. I seriously doubt if you will be able to tell the difference between the prime and the 24-70L, especially at f/5.6 or f/8.