Prime lenses vs telephoto

I recently acquired a Canon 5dMk2 camera.
My old camera was a 5dmk1.

The primary purpose for this camera is to shoot completed kitchens that my cabinet shop produces.

I do most of my shooting with a 24/70L lense and it seems that the majority of this is at the 24mm end of the spectrum.

I am starting to save money for a new lens and I'm curious what would be best to add for shooting interiors. I have read that the "sweet spot" for telephoto lenses is somewhere in the middle of the telephoto range. or in this case 50mm. I have also read that a PRIME lens would produce a sharper image than the equivalent spot on a telephoto, ie. I would get a crisper shot with a 24 mm PRIME lens than at the 24 end of a 24/70 lens.

Is this true?

What would be the benefits of a 50mm PRIME lens over shooting at 50mm on a 24/70 lens?